I think some MIL are a nightmare and some DIL are a nightmare.
I have a lovely relationship with my MIL, we lived with her when my son was born. It was hard at first as she was expecting to 'have' my newborn son and take equal care of him.
As a FTM with raging hormones, my defensive side kicked in and I admit I was really possessive over him. I don't actually think it was a bad thing as it just put that boundary in place right off the mark (thanks new mum hormones 😂). The key thing is, she never questioned my choices or made me feel bad about this.
Of course I let her hold him and play with him and things but taking him for naps, bed, baths, night wakes, taking care of him when he was ill etc was my job, not hers. Im pretty sure I was a bit of a nightmare and she still didn't make comments about it, which I think some MIL would have done. At the same time some DIL would have made an issue about their MIL wanting to take care of their newborn and setting up their own space for baby to sleep with them, change them etc and I didn't I just said yeah we'll see how it plans out when he's here.
We moved out when my son was 1 and now she visits us and stays with us and we get on great. She's always texting me shopping lists for online ordered because she has no clue how to shop online lol. I talk to her a few times a week and send pictures and videos of my son. She loves him and he loves her.
I tell MIL she only drives me as crazy as my own mum does 😂😂 it is sort of different with my own mum though because she loves me. If I didn't have my DS my own mum would still want to call me all the time and come stay with us, I am not sure that MIL would. But I would never let that stop the relationship she has with DS or make an issue out of it, that's just normal surely!
I don't believe in favourite grandparents either, if they want to be in my son's life then they are, there is no favourites, they're all his family.
I hope I can have a MIL/DIL relationship similar to ours if DS gets married when he grows up!