I will natter at you by saying the only people I wanted to be with every hour of every day turned out to be infatuation burnouts, and that people who have lasted in my life could make it to shops, library, and so on, by themselves - that is, were comfortable alone in space for some length of time. I know good marriages get past that infatuation deflation phase. I wish people would get past it before the marriage.
We didn't have children, so I don't have the mother in law experience, except as a daughter in law. With my niece, whom I had some role in raising, now clearly an adult but still, erm, impulsive, which some experts say people under twenty five are (don't ask, I don't know the details). I could go for the throat of her present guy, but she and I have talked about implications of this and that and the other thing. We'll see. (I have various fears that she feels destined to follow a certain route.. time for me to call her.)
On mothers in law and fathers in law: Both of mine rejected me forthwith. I was not only an apostate catholic, but older than their son. We had a good wedding without them. I always liked the father, a man of small years of education (4th grade?) but a reader and a superb story teller. Shy, but interesting once comfortable. Interested in and fairly understanding of human behavior, the perfect present for him being a book on history.
Husband's mother, a piece of work. College grad in a day most women didn't do that. How to put this - not classically pretty. She had many suitors in the war years, and when we dealt with the parents' place, we found many many golden compacts. I don't know what that signifies, exactly. I know she flirted with being daring, but I don't assume past that. She was, in my experience, martially religious, rather like my own mother in assertions. Married the husband after the war. Her sons sympathized with the father and so did I, but I had underlying sympathy for her at the same time I was aggravated.
When she was dying in the hospital and the md came in for the talk with the family, I was the only one to speak up that she had liked the flowers of the day before, as in, no, she was not entirely out of it. The family voted for desist the anti low blood pressure meds. (I didn't vote, not my place.) Well, she recovered anyway. Not much, and she died naturally.