When you're experiencing challenges with your in-laws, step back and take a long view of the struggles. Most kids benefit from as much love as they can get, even if it doesn't look and feel exactly the same between the parents and the grandparents. Speak up when you need to... but step back and let go when you can.
Family unity and healthy interactions, who could possibly be against that? Not many! I've got two daughters-in-law who are precious to me and one more soon to be welcomed joyously into our family. I find myself always trying to be a well intentioned, non-meddling mother-in-law. Sometimes, I even succeed. Sometimes I don't.