My fiancé’s sisters make me want to call off my engagement..

My [27f] fiancé [31m] of 3yrs has 4 sisters. One who actually likes and accepts me in the family, 1 who fakes nice with everyone she meets, and 2 who aren’t good at hiding their extremely judgmental feelings.
Most family gatherings tend to be quite segregated; or I’m just not invited.. If I’m not invited, he tends to just gloss over it and tell me he’s going to whatever family thing I never knew about, and then I usually spend holidays tucked in a corner or playing with the kids/dogs. I’ve tried making casual conversation, befriended them in social media (before I realized you can even block people you’re friends with from seeing anything you post..) I’m at the point where I just try to avoid them as much as possible. Birthdays, holidays, etc., I’m still not invited, and he doesn’t understand why it bothers me. (Yes, I know it shouldn’t.)
One of the sisters got engaged after we did, and has been in a big rush to get the wedding underway - even mailing an invitation to my apartment with only his name on it.

I know it’s ridiculous, and I should just say **** em and live my life. It just bothers me that after us being together for 3yrs, I still don’t feel like part of the family. It’s made me contemplate calling off our engagement a few times.

Source.