The first three people thanked are Avi, Luna, and Shiloh. Avi, of course, is Kristen's husband, so it's likely that Luna and Shiloh are their children's names! This is further supported by the fact that the next two people listed, Grace and Vincent, are Annie Mumolo's children.
No word yet (that I've heard, anyway - movie credits only give so much information) on whether they're twin girls, or a boy and a girl. OP doesn't want to speculate too much.
Avi also has a small role in the film.
SOURCE: OP and the copy of Barb and Star Go to Vista Del Mar that I rented on the Cineplex Store/my friend who has a bike.
As for the film itself, I have never seen anything like it. Go in totally blind, and be bewildered by the absurdity. It's funny, but bonkers. Jamie Dornan is surprisingly good.