My mother in law gave me timeless advice by word and example when I married her son.
She taught me that “he is yours now and I don’t want him back” in word and deed. What she knew and imparted was never interfere in the relationship between your child and their spouse. Whatever you think, it will never work out for you to take sides or criticize their partner and especially not how they raise their child.
It’s ok to be supportive and listen to their trials and tribulations, but it’s smart to keep your personal opinions personal. When they make up from that fight, or fight later, your child may bring up the critical comments you made, and it will come back to haunt you.
Even if the relationship ends, you have to have a good relationship with their spouse so you can still be comfortable at family events so that their children remain comfortable. You want to be included.
I treat so many women whose adult children won’t talk to them at all. They never get to see their grandkids at all. We forget that our children are stuck with us when we raise them. But once their adults, having a relationship with them is our privledge and their choice and we need to behave accordingly, and carefully, as hard as that may be some times.