there's just the two of them, the share a birthday, the sister in my head was 25ish but i can be somewhat flexible there, both of their parents are doctors but they lost their mom when they were young (dimi was 6) and they were primarily raised by their grandmother. their relationship with their dad is 'fine' but not particularly close but the two siblings are close and they're close with their grandmother. it comes sort of built in with a best friend or close friend line with ~schultz that i can fill you in on more if you're interested!