I would have guessed that grandparents, aunties/uncles etc could mount a pretty good case to have care of children should both their parents die.

I would expect my parents to have my kids if me and DH both die, followed by my sister, my brother and his sister (his dad is too old and his mum is dead already).

I guess there must be ways to safeguard this in law, but I would think it would be a hard case to argue that someone who isn't in the family would gain guardianship over orphaned children.

To me, godparents promise to oversee the spiritual education of the child, and that's as far as their technical responsibility goes.

Personally, I would intentionally choose friends to be godparents, rather than family. My family are already interested in my kids, and they will already be ready to look afer them if something happened to us. To connect some trusted friends to my children's welfare seems to me like adding to the depth of their safety net (say my whole immediate family gets killed in an accident, for example).