Girlie, my MIL and SIL have been very involved in my DD's care and upbringing. I love them and for the most part we get on well but I will tell you this: set clear boundaries firmly from the start. I didn't, and can't tell you how much I regret it. Even a healthy In-law relationship can be strained once children come into the picture.
I have very much raised my own child, and I have an extraordinarily functional relationship
with my own mother and family. That said, I have even had to set boundaries with my parents, because they are just a tad overinvoled with my son. They very recently moved closer to me, and this makes things easier, but there were a couple Christmases I didn't have with my son when we lived far apart, because they wanted him and he loves being with them. (They have a marvelous relationship
, and they also do a lot for him.) They also used to get him in the summers and take him on fabulous vacations, which I was thrilled to have him do, but which cut into my time with him.
It was hard because he really enjoys being with them and I am thankful for the love they have for him. However, I finally had to tell them "no" a couple times, because it dawned on me that I only get so many holidays, so many summers with my kid before he's grown up and on his own. Last year, he spent Christmas and New Year in South Africa where his dad was living and working. Once again, nothing I'd ever begrudge my child, but, it makes about three Christmases I have not spent with him.
With a dysfunctional MIL in the equation, it's probably vital that you and DH get on the same page and list your boundaries. I really hope your future child can have a close, normal relationship
with the paternal grandparents, but, they have to abide by your conditions, or else they could find themselves cut off. It's not your fault that your MIL didn't stand up for herself back in the day.