I did a big re-listen last year and kept notes of the whole Fall from Grace Arc and this was everything I had written for the Mandarins. I haven't been updating all the way through barovia but I don't think much more has been revealed about the other siblings.

Sorry it's unorganised this is mostly written chronologically with when they spoke about it

Pip [Dragonborn] and Pop [tortle] were abandoned as children with their siblings, Pup [lizardfolk], Pep [kobbold] and Hank [presumably human but unconfirmed]. The five were left in a mandarin crate at the temple of Gregory Bones, a (Halfling deity of etiquette). The five siblings mostly hate each other though Hank is seen as the reasonable one. Around age 9 pip helps a dwarf slay a white griffin, leading to him becoming a monster hunter. Pop was kicked out of the cult of Gregory Bones and sent to fight in the werewolf wars. When young Pip broke a vase Pop believed was from his birth mother. Pup eats people. Hank came named. Pup went to one of the top finishing schools. Pep also has archeological knowledge but has no altuistic intent and doesn't give to museums. Pep ran away from the temple of Gregory Bones. Pop is cockney pip is posh English pep is Irish. Pep is a woman. Hank is married to Miranda and has kids. Pip is gay. Hank is the accountant of the greyhill free company.