Kinfolk -I kinda came off like Homer Simpson

If your son functions as the sister's father, then you're the grandfather, yep.

As for the cousin thing, I don't remember! I used to know, but in my husband's family all the kids of approximately the same age are "cousins," and all the people from the previous generation are "aunts and uncles." Regardless of actual relationships.

So for example: My F-I-L is the oldest of 9 kids. The youngest is in my husband's generation, and that one's kids are in my daughter's generation. So my husband is called "uncle E.G" even though he's really a first cousin; and my daughter is considered a cousin even though she's .... who knows!

Once removed might be right.

Some cousin info here:

http://en.wikipedia.org/wiki/Cousin

Your daughter and your nephew are first cousins. Your nephew's children are her first cousins once removed.


Your daughter is your grandchild's aunt. She would be step-aunt to the sister and you would be step-grandfather (and would of course leave the step out in conversations) if anything was formallized. Without any legal connection she is probably just a close family friend.

Thank you both...all so confusing!
I must admit sozobe, I kinda like the idea of just calling everybody, cousin, aunt or uncle ;-)