So lost, need a friend

I don’t even know where to begin.. so both my parents are cancer survivors and we had a rough year dealing with all that. Now they both are in remission and good health but that doesn’t mean we are all good. While my mom was dealing with chemo, my parents took in my cousin and some money and items went missing after she left. (Hmm wonder what happened there) well, fast forward to last month. My cousin came back and asked my parents for help. She needs a place to stay and had no where to go. My parents are good hearted people they forgave and forgot. Decided to move on and take her in, they feel sorry for her. I have 3 sisters two younger live with my parents the oldest is married and has a family of her own. All are adults, mind you. Two who are completely infuriated with my cousin living with my parents one who rather live a civil life with her since they all live in the same house. Two of my sisters still live with my parents and my older sister who doesn’t had made my parents life miserable because my cousin is living with them. I’m basically like Switzerland. Not happy that she took advantage of my parents and that is living with them again but also not my place to say anything. I don’t live with them. I shouldn’t care who lives with my parents. I’m so irritated with the fact that now I’m stuck between this stupid drama, can’t get away from it and I feel it’s affecting me. I’m anxious, annoyed and plain out fed up with their bs. My issue is my sons first bday is this weekend, I’m having a little something for him and want my family here to celebrate with us. I’m nervous for my family. My husbands family will come over too and don’t want any drama. I asked my sisters to put their differences aside and celebrate little guy without any drama. This all blew up in my face and now my older sister isn’t coming, my younger sister who hates my cousin might not come and my parents were really nervous of coming of my older sister running into my cousin at my house. I seriously feel like uninviting everyone and just have cake my husband and lil guy and I. I’m so bummed, disheartened and hurt and I don’t know what to do. Sorry for the long story guess I just needed to vent and wonder if anyone ever deal with a situation like this.