I think it’s important to remember that you are a MIL to only one of the pair having the child - you are a parent to the other half. Talk early and often about expectations. We outright asked our S and DIL what they were thinking well before the due date and let them know that we respected their choice whatever it would be. Our DIL has no family in the U.S. so we were the only parents they had to deal with. We were able to be in the air on the way when the baby was born and then hold him when he was only a few hours old. Seeing our S become a father before our eyes was something we can never forget, and having family there to ooh and aah over the experience was priceless for them. We stayed in an Airbnb across the street for a week and only visited when we were invited. We were able to help with laundry and food. I believe we had a mutual understanding of each other’s needs and wants. Started out on a great foot.
@igloo oh, total BS, I knew it, DD knew it, my DH struggled with it being an issue and I told him not to worry and not to make it an issue that once the baby was there, they would be calling, I did not expect an early labor call 
I knew the situation well enough and was in close enough proximity to adjust that I put aside my normal desire to plan and have things figured out in order to not make it “a thing.” Because I think if SIL was forced to take a stand, he would be unlikely to back down easily, but if it’s not a thing, he can see reality when it hits. Being chill about it made him grateful for our presence <3
@somemom, that reminds me of a call I had with my mother just before a last minute high stress event. When I first ask her if she wanted me to arrive a few days before my family to help out, she said no. The next day she called me saying she didn’t know what she was thinking. Yes, please come early.
@youdon’tsay bff, I’m glad you had a good conversation with your S. When my first D was born my local in-laws visited the next day. I asked my (flight necessary) mother to wait until the weekend before H went back to work, but she stayed for a week. I’ll have to ask her sometime if that bothered her. She never mentioned anything.