How am I supposed to let my MIL babysit??

Sorry for the long post but I’m super pissed right now.

Ok so I’m pregnant with twins and I’m very excited! So is everyone else. But I have VERY specific things I want to do with them as far as putting them on a schedule and what not. I work for a school so I have plenty of time off but I’m due in November. I literally have everything planned out to a T (I know babies are unpredictable, I know plans don’t always go accordingly, so please save the “ya right you’ll find out that your plans mean nothing “ comments). I will go on maternity leave which will run into Christmas break then go back for the second semester and my SO will then take his 8 week paternity leave. By then the babies will be about 4-4 1/2 months and go to daycare (which I have already found and enrolled) for about 2-3 months. Anyway all this will depend on the twins getting on a schedule... FAST. Well this week I’ve been babysitting for my SIL who just had her first in December because my MIL is at my house painting the twins room for me. I am the oldest of 10 kids so I know my way around practically any kid you hand me. Well my SO and MIL got back late last night and I woke up this morning to take care of the baby. Everything was going fine up until lunch. I fed him his baby food as instructed then made his lunch bottle (he’s holding it by himself now so I gave it to him and went to wash his dish from lunch) then my MIL decides that she’s gonna go feed him. That’s fine whatever she usually babysits so I just assumed she missed him and wanted to spend time with him. Well in the middle of his feeding she says she’s gonna take home upstairs and change him then lay him down (I assume she’s going to give him the rest, right?....) All I hear from the room is endless screaming and fussing. This goes on for about an hour then I ran out to run an errand come back and don’t think about it. I ended up laying down cuz I had a headache and when I woke up she’s feeding him food again. I say that he’s not supposed to have anymore food food till his mom gets home and she says he didn’t hardly eat anything before. I asked about his bottle and she said “he ate less than half”! (That’s why he was screaming for an hour because he was fucking hungry and you’re trying to make him sleep!!!) All she said then was “oh well he’s gettin this”. This just pisses me off! How am I able to keep this child on a strict schedule all week according to what his MOM wants and she comes home one day and fucks it all up!?!? How am I supposed to trust that she’ll follow my schedule when I’m at work and my SO is watching them? Cuz I KNOW that’s when she’ll try that shit! She has no regard for what the parents want for their children, it’s only how she thinks it should go. Just yesterday she saw a pic of my niece and and called up my SIL and literally said “what possessed you to cut her hair so short? It looks awful“ like seriously!?!? It’s not your child! Get over it! I’m going to have a VERY HARD TIME leaving my kids with her.