Mommy Issues

Ma
So my mom is extremely bipolar. I'm pretty sure she has multiple personality disorder as well. I'll explain my reasoning later on. Tonight was the last straw for me. My mother verbally and emotionally attacks me and my sister to the point of we're both on antidepressants and anti anxiety medication. My sister and I have both had our downfalls, but I'd have to say we're both doing quite well for ourselves. That pisses our mother off. I'm 23, married, no kids, I'm a waitress & licensed cosmetologist, I was a fireman for 5 years until life started getting in the way, and I'm also in the process of opening a salon that consists of 2 private suites that I'm literally remodeling from the floor to the ceiling out of my own pocket. My husband runs his parents restaurant. We have it made for the most part. Besides the fact we've been TTC for 2 years, and unsuccessful which is stressful enough without my mother going fucking psycho on me every 4-6 months. Now, onto my sister. She's 31, a single mom to my beautiful 8 year old niece, working full time as a paralegal at the firm she's worked for the past 5 years, and she just completed AND passed her first year of law school. Superwoman status right?! Aside from the fact our mother has pushed us both to our breaking points, we're doing well. Tonight at dinner , she asked my dad how my grandma was doing. My grandma suffers from Alzheimer's. It's progressing slowly, but it is progressing. My uncles live with her, and family is in and out of her house daily. I planned on going to visit her for a week in June (she and my dad live 5 hours away from us), but someone at my server job is having surgery which means I had to cover their shifts (I need the money for the salon). Also, I have to have my salon completed before July 1st, and my landlord just signed my lease today so I can begin working🙄🙄🙄 My mom looked me and my sister in the middle of a restaurant and said "I'm only telling the both of you this one time. Y'all need to go visit your grandma." She said it in such a hateful tone towards us in front of my niece, my dad, my stepdad (her husband), and the whole fucking restaurant we were in. I said "I wanted to, but everything at work and with the salon came up so I haven't been able to get off work." She said, "I don't care you can get off work. I'm gonna call Jackie" (my MIL who owns the restaurant like she gives a shit what she says she knows how mom is) I told her, "You go right ahead. You do that." Well, that just added fuel to the fire and she had the audacity to bring my husbands grandmother into this saying we would drop everything to see her. She lived in Greece and passed last year. We honeymooned there, and visited with her which was the first time I ever met her. My husband met her 3 times his whole 28 years. It was such a low fucking blow. She always brings his family into it.  His family actually invites me to things. My mother didn't even care to invite me to my nieces VBS recital thing tonight. She never invites me to anything. Ever. I'm to the point I just wanna give up. Everything's been going great since my sister started law school, and now that she's out for the summer moms starting losing her shit again. She told my sister she was gonna help with the last $4,000 she owed for law school, and she's supposed to be paying for the flooring in my salon which is only like $500. I'm trying so hard right now to just suck it up because I'm 48 hours she'll be acting like nothing ever happened, but it hurts my feeling so bad. I know if I open my mouth she'll back out on helping with the salon. I need all the help I can get, but I don't want her to hang it over my head like she does everything else. It's so hard for me to just get over this every time it happens. It drives my husband nuts when she does this to me, and if he witnesses it happening he always defends me. My dad and stepdad know it's a lost cause. Hell they've both been married to her. I just don't know what to do here. Has anyone ever dealt with a parent like this? Any advice would help. I love her to death, but I just can't anymore.