I have just the one younger sister. And I have a stepsister who is same age, aaand another stepsister and stepbrother who are both much younger than the other two. I don't live with any of them right now, though I think the eldest may be moving over here after finishing her a-levels and possibly going to the same uni o:
I get on with her better than I do my biological sister, really. probably because we're not sick of the sight of each other yet :v plus she'll watch rubbish telly with me, which is very kind.
so.. I don't know. I'll say 2 siblings as a sort of compromise <<
that's enough for me, though. I have eight younger cousins all on one side of the family, so at times like christmas i get my fair share of chaos.