Just for the record, I'm on my third wife (yeah, I know). I hope I've learned a lesson or two along the way.
My current wife's parents are exceedingly generous to my children and grandchildren just because I married their daughter. It's embarrassing that they treat my kids better than do two-thirds of my own family.
And it's bad enough that some in my family don't bother with my kids, but on top of it, they pull crap with my kids (and wife #2 sometimes) just to poke a finger in my eye. I think I'm a pretty good guy, and I can take a pretty hard hit. But leave my kids out.