Fiancé mom and sister talking shit !

Ladies tell me if I’m overreacting and let me give you a little back info so it will make sense why I’m keeping my distance from his mom and sister until we have a real talk. After becoming engaged and a few times before I tried to get to know my future mother in law and sister in law better so I invited them out for lunch,got them gifts for their birthdays,went to family events at their house etc now mind you neither of them even said boo on my birthday and yes some of you might say well maybe they didn’t know it was your birthday .. ok but if he wanted to stress to me it was their birthday why he didn’t tell them it was mine but that’s another story. Fast word to after the engagement his mom and sister start saying we weren’t ready because we argue now mind you the mom husband is cheating and the sister can’t get her man to propose but they have so much to say about us. He told me they said other negative stuff about me so I said ok I won’t go around them because idc that they said negative stuff but I refuse to play like I don’t know. He apologized for allowing me to go out my way to be nice to them and try to build a relationship but now he wants me to go around them saying oh they didn’t really say anything that bad ... ummm sir you can’t say they talked shit but now because you want to show up to events I’m supposed to forget what you told me. I told him I won’t go over there unless we all sit down and talk about what I know because I need them to know I’m aware. It’s been over a year and I haven’t seen them and he seems to want to bully me into dropping it but how can I