I love my fiance and his family dearly but I got a request from my MIL to include his sister, half sister (along with her husband and daughters), and brother in the wedding party. I'm not comfortable with this for a reason which includes not being close with his sister (I tried while I lived near her but I felt like we didn't click personality wise) and I haven't met his half sister yet. I also asked people (my best friends who are like my sisters) to be a part of it because they're the few people I trust to be there.
I think it's because she wants it like his half-sister's wedding which is a bit frustrating. I already want to ask his sister to read a special reading and his brother will be an usher. How can I address the issue without ruining relationships?