I don't want my future children to spend significant time with my future in-laws
Are you serious about this right now? What kind of relationship do you have with your future in-laws?
I don't have one really, but I'm sure I won't like them.
I don't think it is right to keep grandparents away from their grandchildren just because you don't like them. I think you should try to find some common ground and get a long for the sake of the kids.
Fuck them, they won't even care.
You don't even know if you'll dislike them yet, so why are you acting this way? Most people would believe that you're being very petty and annoying right now. Is that how you want to carry yourself?