Sister-in-law Inclusion in Wedding Party

Hey all! I was hoping for some advice on how to approach this situation — I am trying to do so politely and conscientiously. My fiancé has two sisters, one of which got married a couple years ago and did not include the other sister in her bridal party. At the time, this was a major point of tension within my fiancé’s family including arguments, his mother crying at a family gathering, etc. I had felt so bad for the excluded sister at the time that I assured her when/if my then-bf and I got married, that she would be a bridesmaid in my wedding.


About a year after that, the excluded sister came to visit my fiancé (then-bf) and I and said multiple comments about me that I found offensive. She also was very pushy about our potential engagement plans. My then-bf talked to her about it at the time and she apologized, but I honestly haven’t really spoken to her since. As for the other sister, we are amicable but she once was rude to me when she was drinking like 6 years ago and I’ve always felt a bit off around her since then. I also just want to say that overall I am fine with his sisters and those are just instances that I think influence how I feel about including them in my bridal party.
It’s very important to my partner that his sisters are included in our wedding. I think he was hoping they would be bridesmaids. But after thinking it over, I do not feel comfortable enough with them that I would want to include them on my bachelorette trip or have them around when I’m getting ready on my wedding day. I tend to be an anxious person, and I would like the people around me to be ones I feel comfortable and confident with.
My proposed solution was for my fiancé to make his two sisters be groomswomen and I would have my sister be my MOH and my brother be a bridesman. Two and two — thought it was only fair. Unfortunately, my fiance is hesitant to agree to this and called it a “sensitive topic.” I think he remembers how upsetting his sister’s wedding was to his family and does not want a repeated situation. I completely understand that and do not want to upset anyone either, but this is my personal boundary. I also know his family is likely expecting his sisters to be bridesmaids especially after what I said and I don’t want to hurt anyone. My other issue with them being bridesmaids was simply the unfairness around them taking two spots from other friends/family of mine while I would only have one brother being a groomsman.
My question for you all would be, do you think including them as groomswomen would be poorly received by his family? And if we were to make them groomsmen, how would it be best to explain the reasoning behind that decision? Also, do you think my idea of my fiance and I each having our two siblings on our prospective sides makes sense?