In-Law Problems, i don't know what to do

My Fiancé and I have been together for 6 years. My fiancé brother and baby momma all got along and would hang out all the time then just recently my fiancés brother and baby momma split. Mind you, they were young parents 20-21 that loved to party and drink. I watched their daughter a lot I was her babysitter when her parents were at work and wanted to go out. Aside from that I grew a very close to his brothers baby momma, I could talk to her about anything. After they split he immediately was in a relationship with another girl, that also had a kid. We've notice my fiancé mom will go out and do things with her but she has never once invited me anywhere...When my fiancé proposed (at their house on xmas) no body official welcomed/hugged me or even congratulated us they just carried on cleaning up the mess from the wrapping paper. And Well my fiancé family started bashing me, and blamed me for everything that the baby momma found out. And she always found everything out herself I never had to tell her. Things got so out of hand that someone opened a CPS case a against the mom under my name! And we found out because she had me as a reference so the workers called me asked me if I had concerns and then said the story didn't add up I was beyond furious and called my fiancé and his whole family all claims they would never. It is just so hard to believe anything they say because they know I still talk to my fiancé Nieces mom, and they don't like it. Before issues occurred they always told me not to let their problems ruin my friendship with her. I am just so hurt on how my fiancé family has been towards us and just distant themselves from us. Mind you that my fiancé brother was a mommas boy and her everything, it was even to the point that she was telling him to fight for custody and giving him the money to do it, paying for the lawyers and all. He would literally read the text between his baby momma and him when she would try to confront him about an issue, and he wouldn't know what to do. And well I know nothing will be the same and trying to plan a wedding makes me not want to have one because of all they problems and knowing they will be going out of force because it's their son. I bring myself down a lot when I hear other couples get along well with their in-laws and even go places with them without their S.O. because all I ever wanted was to gain a good relationship with my in-laws, and now I just don't know if it's even possible because I feel so betrayed that they think of me of the person who goes and tells the baby momma things about them, when it's their other mutual friends she still talks to.

Do I just leave it and continue with my life and not make it seem like such a big deal. Do I let them be and just keep blaming me. Should they even be allowed to be at the wedding 🤷🏼‍♀️