This is a difficult one for us as all our family lives in another country. However my sister and I have agreed that if anything should happen to either of us, we would take each others children. I know if anything happened to my sister and BIL that my mum would expect custody of her children as they are very close, but as my sister pointed out my mum is a smoker and that is not a situation she could put her children into. Ditto for me if something happened to DH and I, his mum is very old and my mum is a smoker. My brother is living the single life and DH's siblings are not the sort of people we would want our children with as a first choice, so it would have to be my sister.