My in laws has basically shunned my husband (their son/brother) and our whole family from theirs. We married in 2011 with my step daughter (3 at the time) and my daughter (8 month) since being married my husband has adopted my daughter and we have had another daughter. My children are now step daughter (5) daughter (3) and daughter (1).
His daughter came from a previous "marriage" which happened as teenagers and ended as teenagers due to his wife having multiple affairs. During the time of their relationship she spoke some to his oldest sister, trashed talked his middle sister, and partied hard with his youngest sister (who was much younger than she was). After the divorce she continued to party with his youngest sister to stay in his business but they had a big falling out. The whole time we were dating I would feel a little strange going over to his moms (my now MIL) because all his sisters would talk about was his ex. They would trash talk her non stop. One even said the next time she sees her she was going to beat her up. They were all so excited that we were getting married. One of them did my hair at my wedding and the other did my make up.
About a year after we were married I started to notice my MIL relationship with his ex. My MIL was married for 18 years and had an affair on my FIL but has not been married to her new husband for 10 years. Both my step father in law and my step mother in law are great people and I love them dearly. I assume that the relationship between my MIL and the ex developed because of that similar trait. My husband deployed just shortly after our 1 year anniversary. I was 17 weeks pregnant at the time with our baby girl.
During the deployment I was told that my step daughter was never allowed to come over. The only time she got to see her half sister was when my FIL and step mother in law would have her and they would call me to come over. Once the ex found out about this she no longer allowed my step daughter to go over to the FIL house. My step daughter would stay over at my MIL almost every weekend and I was never invited to come over. The only times my MIL would call me was to tell me something I needed to do for my husbands ex. She would visit with her and go out to lunch with her. She even invited her to family Christmas parties and didn't tell me about them. When my daughter was born she told some of my aunts and uncles that I wouldn't let her see the baby?! Which seemed ridiculous since she had just been to the hospital to see her. On the way to the hospital to see my daughter she called the ex to inform her that I had the baby but she did not want to bring my step daughter to meet her new half sister. They would write my husband terrible letters about me that he would let me read full of lies. I was never invited to anything except one time I was invited to drive over an hour to go to a bounce house when I was 8.5 mo pregnant with a 2 year old so obviously I was unable to go. I paid for my step daughter to take dance and I was told I could only go to the rehearsal not to recital. I was not invited to her pre K graduation or her birthday party. I spent many nights with my 2 year old missing her and I even put together a slide show of her for my 2 year old to watch when she missed her.
The first month that he was home they tried to have us over to their house for a family dinner. My husband refused to go. We invited them to go out to eat with us but they did not want to. He says "when they start respecting our family we will be around them. When they start treating you like my wife we will be around them." I invited them to see the lights at Christmas time but they did not want to go. I invited them to come to the pumpkin patch with us in the fall but they did not want to go. They were invited to the blessing and only my MIL went. I invited them to go to Busch Gardens with us for Halloween but they did not want to go but instead scheduled my sister in laws baby shower that same day knowing we could not go because we would be out of town. But the ex and her mother came! They are all friends on facebook. They take pictures together. They sit together at parties. They scrapbook together at my MIL house. Recently they told my husband that they did not consider us to be family and they did not consider me to be an in law but they only considered his ex as family and her daughter (my step daughter). They make up stories all the time and they take things I say and spin them around to try to create drama between my family and the exs family. They have a family gym membership and my husband's ex and my step daughter are on it but we aren't and our children aren't.
All we do is live our life. If we say anything to them they turn it around. If we buy anything they give us a sap story about how they don't have any money. One time my MIL told my husband that he needed to be paying more child support. His ex works about 20 hrs a week. We don't need them and I think that bothers them. However, I think it would be nice to have them be family since they are my children's family. We teach our children to love one another but it is hard to speak the importance of family when we have family members acting this way.

I'm just curious to know if this ever gets better?