Dame Jenni Murray is an only child, whose “pushy and devoted” mother thought she was going to die while giving birth to Jenni so was determined to never have another child. That meant Jennifer Susan Bailey grew up with a surfeit of adult attention – something which had its advantages, but also definite disadvantages. In this episode Jenni talks about why she wanted a sibling for her own first born, why being an only child left her lonely in her grief when her parents died, and how she thinks she was spoilt by being the only child in the family.

Drs Chris and Xand van Tulleken were born seven minutes apart, but don't know who arrived first! As older brothers to 'Bratty', the trio enjoyed an idyllic childhood with an "anarchic", fun-loving dad and a perfectly complementary mum who worked hard to provide for the family and instilled a work ethic in her three sons. As teens the twins decided to become doctors, and cooperated beautifully to study for their medical school interviews. It was - by their own admission - a rare episode in a relationship which can otherwise be dogged by squabbles and rows: and yet the pair *clearly* adore each other, as highlighted by a recent near-death experience which showed them how dependent they are on each other. Don’t miss their new podcast series on food and weight, which obsesses them both…

Naturalist Chris Packham and his little sister, fashion designer Jenny Packham, grew up in Southampton in a crazily creative and competitive family. They fully indulged Chris's enthusiasms and obsessions, including trekking through nettles and staying out for hours to spot birds or catch newts – while Jenny developed her own interest in art and making clothes, inspired by her dress-making grandmothers. As teens the pair bonded through music and fashion, though Chris's undiagnosed Asperger's made life tough for him and challenging for the family. Jenny's love for her brilliant brother has never faltered – and they remain as close now as ever.

This end-of-season special episode is a veritable pot-pourri of sibling love. We've rounded up Jane Garvey, Susie Dent, Chris Packham, Professor Alison Pike – an expert on siblings – and two very important guests: Catherine's (slightly overexcited) sisters Bex and CJ! Look out for listener messages to brothers and sisters around the world, and bonus episodes in the coming weeks. Don't forget Siblings Day on April 10th...

Eileen and Catherine Walsh grew up in Cork before moving to Dublin to pursue careers on stage and screen. On leaving school, older sister Catherine cried, saying “someone much better was coming” to fill her shoes – but as grown ups, both sisters hold each other in high professional regard and lean on each other for support in a tough industry. In this episode they talk about the influence of the Irish church on their childhood, their dad as a long-suffering theatre goer – and the craic to be had in a busy and fun family home.

The barrister, writer and broadcaster Hashi Mohamed Hashi had 11 siblings: out of them all, he is closest to sister Shukri, from whom he has never been separated despite the ‘tornado’ which scattered their family following their father’s death. Aged 9 and 7, they travelled from Kenya to the UK as refugees – where a new home, languages and culture baffled them both. In this episode they talk about social mobility and success, their love of baked beans, and the strength they found to make it through.

Nick Hornby and his sister Gill both loved books from an early age, spending Saturdays together at the public library. Reading was an escape from a childhood which became ‘strange and baffling’ after their father was more and more frequently absent from the family home. In this episode the two authors talk about keeping each other’s childhood memories safe, teenage kicks, and always looking for approval from one another.

Standup comedian Ahir Shah and his older sister Akanksha (Tash, Didi, Dips) are eight years apart, but incredibly close. Ahir's arrival was like a Christmas present for Tash, who loved caring for him as a baby and still worries about him now - especially when he lays his soul bare on stage. The pair grew up in a funny household with 'giggly' parents, where money worries couldn't take the shine off the fact that their childhood was "good in all the ways it was important to be good". As adults they describe their relationship as wonderful, and are working together on starting to 'parent’ their parents…

Broadcaster Nicky Campbell first met his birth sister Esther as adults, after they had independently traced their Irish birth mother. Both had been given up for adoption as babies and grew up in Edinburgh, and were left with complicated feelings around belonging. In his new book 'One of the Family', Nick tells the whole story of his breakdown, diagnosis as bi-polar and being saved by the love of his dog, Maxwell. In this episode of Relatively, Esther and Nicky tell their parallel stories and reflect on questions of identity, family – and the bond they now share as siblings.

Anna Whitehouse – aka Mother Pukka – and her little sister Karen Whitehouse (creator of true crime podcast "Who Shat On The Floor At My Wedding?") got off to a fractious start as siblings, with episodes of bum pinching, shin kicking and trolling through poetry. But something altered on a family holiday, and since then they have been incredibly close: “the ying to each other’s yang”. Karen (Anna’s self appointed life producer) pieced her big sister back together again after miscarriage and post-natal depression, and Anna is forever grateful to her “much funnier”, incredibly kind and patient sibling.

Baker Briony May Williams (Bri, Brizzle, Braz or Chewie) has two brothers, Max and Ben: they come as a pair and operate like "a comedy duo," so for the first time we have three guests! The family are close geographically as well as emotionally, and all live within 10 minutes of each other in Bristol. Briony has been on a bit of a journey since her star turn on GBBO and now speaks openly and boldly about being disabled - a big change from childhood, when the word was avoided. The boys are protective and proud of their sister, who was diagnosed with depression in 2010: now they keep a watchful eye on the 'Brio-meter' in case she ever needs cheering up. In this episode the trio talk about looking out for each other, being the men of the house – and the politics of the school bus.

Actress Julie ("Fernacka -Pants") Fernandez and her big brother Rab were not always as close as they are today. Their larger-than-life dad Barney could 'light up a room" and dominated their extraordinary childhood, moving the family around the world and creating a technicolour life – which could be thrilling, but was often unhappy and sometimes violent. At the same time, 'diddy' Julie's brittle bones meant endless trips to hospital, enduring 70 operations and months spent in plaster, something she knows Rab also found difficult. Despite everything, their relationship is now rock solid – and one in which they both find complete trust.

Chef Rob Aikens (or 'Mounds') is 5 minutes older and one inch taller than his twin brother and fellow chef, Tom (or 'Eggy') . As children the duo who were "joined at the hip" were known as Double Trouble in their Norfolk village and caused havoc at school. A talented home-cook, their long -suffering mother taught them what good food was, and how it should taste – but inspiration to make a career in the kitchen came like a bolt from the blue one family holiday, and from then on there was nothing stopping these ambitious brothers. In this episode, the pair talk about being very, very, VERY naughty, standing up for each other and coming to terms with a life that's now spent apart.

Before taking up running, Cory Wharton-Malcolm (or 'Beefy') was 'fat and unhappy in his own skin' – something his sister Janeen Wilson was totally oblivious to. She only ever saw her cool older brother, who had precious little time to spend with her. Fast forward to the present day: psychotherapist Janeen and coach Cory are now very close (she has her own keys to his house) and running has helped Cory to both deal with the grief of losing his Gran – who raised him and Janeen – and given him the platform he wanted to try and make the world a better place. In this episode of Relatively, Cory and Janeen talk about fitting in, silly voices, and feeling truly at home with one another.

Ruby Wax's daughters Maddy and Marina Bye grew up in a household stuffed with performers where "nothing was normal" and being funny got you lots of attention. Now Maddy ( "I give nickames, I don't get them" ) and Marina (The Beaver) are a professional comedy double act named 'Siblings'. They feel invincible together on stage, drawing on lessons learnt at drama and clown school and pointers from greats including Rick Mayall and French and Saunders. In this episode of Relatively we talk about mental health and chutzpah, experimenting on your younger sister for fun, and getting career advice from Alan Rickman.

Historian Dan Snow's greatest regret is how he treated his little sister Beck Snow in childhood, though the duo (despite being separated by the Atlantic) are now as thick as thieves. In this episode of Relatively, Dan and Beck recount the summer they learned how to wow the dance floor at teenage parties and the soap-opera-like moment they found out about their father Peter Snow's love child Matthieu. The siblings talk about teasing, eccentricity and fame, privilege – and the pride they feel for each other's successes.

Johnny Flynn (nickname Stumblebum) has a little sister Lillie (nickname Squirtface) as well as four much older half-siblings – and the performing gene, inherited from their dad Eric Flynn, runs strong in all of them. As children Johnny and Lillie were thick as thieves: he loved nothing more than making her laugh, so winning a choral scholarship to boarding school at age 8 and leaving her was a real wrench. In this episode of Relatively they talk about living together as drama students, searching for peace after their dad's death and performing on stage together in Johnny's band, The Sussex Wit.

Divina De Campo is one of seven: her childhood nickname was 'Rent-A-Wrecker'. Born Owen Farrow, Divina came out as a teenager and now makes a living from drag, appearing regularly on primetime TV including finishing as first runner up in the inaugural season of RuPaul's Drag Race UK. In this episode of Relatively, Divina and her sister Carys Cliffe talk about the teasing that goes on in a big family, the perils of Section 28 when you're being bullied at school – and the thrill of getting to the end of My First Piano book.

Jess Phillips MP is the youngest of four, the only girl and cheerfully confesses to being "the bossy one". In this episode, she and her brother Luke Trainor talk about getting into big trouble as kids, whether or not you were allowed to smoke in the loft (you weren't) and how even as adults, they still have each other's backs: Jess tried to help when Luke suffered from serious drug addiction, and Luke worries about Jess navigating an increasingly fraught political world.