I was the DIL in a similar set up but there was no baby involved. While my MIL can be a head fuck and draining she is a decent person if a bit on the overly holistic side of life.
It was hell living with her. First few months were absolutely fine. (We also paid market value for the room with all utilities and council tax included in the price)
The rest of the two years were difficult. She would often get involved or offer advice that wasn't needed or wanted if we as a couple had a disagreement. She would make off the cuff remarks about us spending money on the odd take away or bottle of wine. Or if we booked a holiday etc
My advice don't give an unsolicited advice especially when it comes to baby. Let them come to you if they need anything.
Also, things like not having enough cupboard and fridge space was tough, we are also much todoer than her and I felt if I wasn't at work I was cleaning.
Felt that we couldn't make any noise after a certain time in the evening, just in case we disturbed her. Took the fun right out of sex as well. Just awkward if she woke up and used the loo or was getting a drink.
Laundry was always challenge, she didn't have a washing machine and only two clothes horses. Seeing my pants drying in the kitchen while cooking dinner would fuck me off and I always smelt of food. Been told I didn't but I knew that I smelt of cooking smells.
Would be woken up early at the weekends when she would randomly decide to clean or talk very loudly on the phone and we didn't feel we could complain or doing anything about it, it is her house after all.
We both smoked at the time, (early 00s - still socially acceptable and smoking was still allowed in doors everywhere) we would smoke outside, but then had to listen to lectures on smoking and everything that came with it. I know that came from a good place - but trust me smokers often know more about the damage they are causing to themselves than others can tell them.
How will you deal with or turn a blind eye to their habits and crutches?
Social life was difficult because although we could have friends over, we felt they had to leave by 11 pm at the latest. She would complain she could hear us laughing from her room.
We never used the living room. Bathroom, kitchen and then up to our room. It was shit feeling like you could only live in one room, because you know you can shut the door and dont have to fake socialise after a hectic day or when the tubes would malfunction.
Never felt we truly had our own space. We bickered and argued alot as a couple. Felt stagnated and trapped until we had enough money for a deposit. Not sure how we made it through and didn't divorce.