I need advice

My mother in law is having to move back to Louisiana from Texas for work since her husband lost his job. She’s asked to stay with us but made it clear she understands if we say no and understands how big of a decision this is. I can tell my boyfriend is all for it. Of course its his mother but he’s also said it’s ultimately up to me even though he’s already made plans on where the kids would sleep and what not... that’s my biggest concern. My kids. They aren’t biologically his and we haven’t had the most stable past especially after my divorce from their father. We finally have this stability and security in this home and Im reserved about breaking that up again by having someone live with us ultimately taking away one of their own spaces for her to stay in. My other thought is im due with our child beginning of October. When I speak of unstable past I never had the “proper” coming home with a baby. It was always someone else’s home I was currently living with. I was so set on finally doing things right with this baby. I have my own home to take her home to and be alone as a family with stability. In the back of my mind it’ll once again feel like I’m living with someone if his mom is here. I also consider that she will be able to help out when she’s here as my boyfriend works in the oilfield and is gone a lot. Also that she will be working two jobs and hardly here besides to sleep and her days off. I just am torn on being the bad guy who says no, if I morally should help her out, and regretting saying yes when it’s too late. Do y’all have any advice for me?