So, this is difficult. This stuff is for a lifetime. You are marrying her. SO, you follow what you say in your vows. You are attaching to your wife, cleaving to her. This means that outside of the marriage, you can not let anyone get in the way of the marriage. That includes your family. You can tell your sister, for example, if you want an opinion on something, you will definitely ask her. Otherwise, you do not want the opinion. You love your fiancé and plan on a happy life with her. And things are going well. DO NOT talk to them about her. You need to vent? Keep a journal, ask a buddy, etc. But if they already feel crummy about her, don't feed it. And same goes for your fiancé. Try to just not talk about each of them to the other. That is definitely fuel. You get it off your chest and then they have that info and keep using it.
What is very foolish about your family spoken as a woman and as a mother of boys, is that your wife soon will have all the power. They are the 'in laws'. She has her own family. She's now creating her own with you as her husband. And if they are negative, she will begin to resent, distrust and pull away. And that can be forever. And as she needs them LESS in her life, they are the in laws, your family will be cut out more and more. In a lot of relationships, wives have great control over where time is spent, with who, how well kids know grandparents, etc. I plan on being so nice to my future daughter in laws that they will never want to push me to the side.
Your job is to be on your wife's side. The more you do that, the more things will come together for them to get along. She will do things with them and for them because she loves YOU> Not because you make her feel like she has to or she feels trapped in bondage with them.
When I got married, my in laws did not go to my husband about wedding things. I was planning. If they had, I'd feel like they were going around my back and I'd resent it. Especially if I thought they didn't approve of me. Tell them they need to respect HER. SHE is your future wife and they can communicate with her directly.
And your wife is irritated. And if you waffle and stick up for your family over her, she'll start to see you viewing them as more important than her. She has a history with her ex's family that must have been positive. She's not got that with yours yet. It's not been great so far and people don't make an effort for things that aren't feeling good to them. What you can do is tell her that you love her. She's your number one. You will be family, the two of you. But it does hurt to think that you will be less involved with your family in the future if they can't get along. That you will talk to your family and be on her side. But to please try to also forgive them.
Don't dare tell your sister (one with child in play) that your wife is keeping distance. That is fuel to the fire. Just say she is busy if she doesn't go.
But had you stuck up for her, been on her side, not the go between working both sides . . . she'd be less resentful of your family. good luck
Also she thinks just because her family dynamic is different from mine as in her family come visit more often call more often etc. etc. that her family is better than mine's which I told her I'm perfectly fine how my family operates. That I don't need my mom and all my sisters and brothers calling me every day. I have no psychological issues of how I was raise or anything like that my mom work 4 jobs so we don't live in bad neighborhoods. She owned multiple houses and very nice neighborhoods. Just because your family structure is different than mine doesn't mean we're not family oriented.