BPD mother and upcoming wedding - abusive past and present

I'm 28 years old and have a 30 year old sister that doesn't speak to my mother anymore and hasn't for years. Nobody speaks to my mother anymore because of her abusive behavior. She used to be awful, but she clearly picked me as her favorite, in a terribly unhealthy way. It seemed like she was obsessed with me and was unwilling to share me with family, often threatening suicide if I saw my dad or spoke to my sister who by high school had moved out. When my parents got divorced, I was 10, and my mom began to abuse my sister...physically, verbally, emotionally...she slept in the basement every night. I slept in our room. She sometimes wasn't allowed to go to school. She was told to destroy my dad's house, and my sister was terrified of my mom so she made messes and scratched up my dad's car, and my dad for some reason never put two and two together when the DCF and police showed up at our house over and over and over. When my sister was 15, she moved out and never looked back. I stayed with my mom and wasn't allowed to see my dad. Sometimes I feel so guilty that my sister took the brunt of the abuse, but then I know that the way my mother treated me was awful as well. I remember her holding a knife to her throat as I was on the phone with my dad, calling him awful names as she instructed me what to say, scared that she would kill herself if I did not. I remember hours and hours of her screaming and screeching and name calling and throwing things because I didn't offer to make her coffee enough or I was rude or inconsiderate. I remember being locked in the garage or the basement when she had fits of rage for whatever reason. I remember the day I got picked up from school after my freshman year of college, she was screaming and swearing at me to hurry as I was running, crying, and carrying all my stuff to the car alone, making a huge scene. I was humiliated. The drive home was terrifying. She even dropped me off on the interstate and drove off. I was either the most wonderful angel or the most horrific, thankless child. The worst part for me was the relationships I didn't have with my family growing up because of her.
I still have a relationship with my mother. She's pushed everyone away and I was really the last one around. I know I stick around because of guilt. I talk to her almost everyday on the phone, despite the fact that it is often an emotional burden. I drive an hour and back twice a month to see her, even though I dread it. My mom is not like she used to be. She is manipulative and still guilts me. But she hasn't seemed evil in a long time. She's also in a wheelchair due to a knee replacement she never healed from (I don't believe she ever wanted to heal. She didn't do the physical therapy and she always as long as I remember had "health problems" like cancer and MS (none of which was real)...she needed to need me and needed me to know that she needed me.) But I haven't been able to stop being around for her because of guilt. Besides, she literally has no one else. She has a third daughter who also hasn't talked to her for years (my half sister) and she doesn't speak to any of her family.
I've sort of just settled on the fact that she will always be a part of my life, and I can't totally cut her out like my sister did.
Things have sort of reignited because I am recently engaged. I am terrified of my mother being in the same room as my sister and family, for my sister's sake and for my own. I know she is capable of making a scene and ruining the wedding. My sister has said that she will be civil of course and it is my day and that's most important.
My mother has been trying to contact my sister again, despite my sister's ignoring her for years. My sister finally responded yesterday saying that she does not want to speak to her, and she needs to stop texting her. My mother sent her the most horrific text message in response. Awful name calling, ridiculing, just the most repulsive horrific thing I've read in so long. And it brought everything back for both of us. I don't think it is even fair for me to invite my mother to my wedding after that, not that any of those things are new, but it's like...that version of her was just gone for years, and it came out so strongly in that message. It's almost like I forgot that part of her. I don't know what to do. Part of me feels like I need to have my mother there, it stings my heart to think of not inviting her. But I can't even imagine getting married and feeling like I could enjoy my own wedding with her there, not trusting that she wouldn't mistreat people.
I 'm just not sure how to handle this.



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