Well, I have a little bit of experience with this. I have an excellent relationship with my family, and my husband does as well (although he is not fond of my father at all)
However, my husband does not have a relationship with his mother, and he keeps her away from me at all costs. She is an incredibly selfish person and she is manipulative and underhanded. For example, at one of her son’s weddings, her first comment to her new daughter-in-laws parents was “So, does your family have any history of mental illness?”
She sends my husband nasty text messages followed by ones where she professes her love for him. It is plain STRANGE. She asked for my phone number at a family function and my husband stepped in and refused.
It does strain my relationship with my MILs parents though, who don’t see all her bad behavior and just think her kids and daughters/sons in law are just plain rude and disrespectful (they all keep her at this same distance).
However, we manage to have a wonderful marriage despite that. We still attend family functions, going in with a gameplan for if things go wrong (and boy, do they go wrong) but the important part is that we stick together and we always have eachothers backs.
I think that having a wonderful support system is helpful, but I think that paramount to that is the strength the two of you derive from your marriage to eachother.
I don’t know if that is what you were looking for, but I hope it helps! Just remember, we don’t get to pick our family, but we do get to pick our friends! In some cases, the latter is healthier than the former!
ETA: My husband also refuses to allow my Mother-In-Law to babysit the children. Period. She once (in an arguement) said to him “Don’t you want me to have a relationship with your daughters?” to which he responded “Hell no”. My sister-in-law (the only other one of us who has kids) also does not let her watch the kids alone. She just can’t be trusted, plain and simple.