Crazy MIL Need Advice (long)

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Some background. My son (different father, he is 10) and I live with my SO. MIL and I used to have a decent relationship. We'd talk all the time and once I got engaged to her son and also pregnant, we'd talk about weddings and baby stuff. I don't have parents and I'm just now starting to talk to my grandmother again because of drama surrounding my mom's death when I was younger. So MIL is the only "motherly" person in my life right now. She prides herself on how blood doesn't matter and you and your son are family blah blah. SO and I decided to move to the town MIL lives in so it would be easier on both parties once the baby is born (February). SIL lives there as well and is also pregnant (April) so we thought it'd be easier for her not to have to drive to a different town to see our son and what not. We would be renting out a property from her until we could save to buy our own house and we had some concerns and boundries we wanted to discuss with her as she is a very controlling and intrusive person. She knows this and is proud of it for some reason. As soon as we got to her house she was immediatley defensive and took everything we said as an attack, only listening to respond and deflect instead of hearing anything we were saying. We never attacked her or demeaned her in any way, just tried to explain the birth plan we had and visitation after baby is born for the first weeks. She flipped out and told us to get out of the house we're at now (we are renting a property from her in the town we live in as prices here outrageous) and she was cancelling the baby shower and "shit's going to change around here" blah. So we went to a mobile home place and bought up a house we could afford and started looking into a one bedroom to stay in until it was delivered (January). She came over that night at 10:30 screaming and hollering about the same crap we were trying to talk to her about earlier. She started to attack me personally and my family (I have a difficult past with my family and I have told her about a lot of it) just throwing stuff in my face and being just rude. I snapped and started to raise my voice but not completely yelling as to not wake my son up and she said if I weren't pregnant and SO wasn't right there she'd beat my ass. She's almost 50 and I'm 29. She and SIL stopped talking to us for a while. SO and her have since reconciled and are talking all the time. She has always called him every single day since I've known him (since high school). So they're back to that. She still won't talk to me except for through my SO. She has to go to EVERY one of my ob appointments, which I think is weird, she demands to be in the delivery room. I have already explained how uncomfortable it would make me feel if she were there but she doesn't give a crap. She's again throwing a baby shower and not kicking us out anymore. She's upset we won't be moving to the town she's at anymore.

My question is, what the hell do I do? I can't take this woman anymore. She is bipolar as hell, she's the most controlling, micro-managing, passive-aggresive phsyco I have ever met in my life and I tell ya, I have been around some crazies in my time on this Earth. She no longer speaks to me but expects me to just be okay with all her intrusiveness into our life and birth of our son (his first), because she's the grandparent. She told me pretty aggressively that her grandkids aren't grandkids, they're HER KIDS. Which worries me because of how she is and how she goes behind my back to scheme things (stories in themselves right there). She will call SO (works in the oilfield so isn't home much) to inquire about baby stuff that only I'd know because I'm carrying him, and will need stuff done or whatever that he can't do because he's on location but I am fully capable of because I am home after work. We have both told her to just text me because it'd be easier and he'll forget because he's busy (duh he's working) but she refuses. I don't understand how I am the bad guy in this still. I am tired of her holding the house we rent from her or the baby shower and whatever else she can, over our head. She has nothing to do with my son anymore. I know my SO is tired of the fued and I try to ignore her but it's hard when she's just right freaking there, passive-aggresivley being a bitch. There is sooo much more than just what I've written but this is already long enough. I have more examples if need be. I just need some advice because she is single handedly ruining the excitement of this baby, our engagement, and our first house we bought together (since we had to rush that). We also have gotten into fights because of her. I have tried to be the bigger person and re add them on Facebook (MIL and SIL deleted me) the SIL is up MIL's ass and gets herself involved so we no longer have a relationship either fyi. I try to converse with them and be polite but I'm about to go insane. They're both on here but I'm at the point where I really don't give a shit.