I think Mother-in-laws can offer some advice, if they realize they it might not be heeded. I am a mother-in-law twice and a grandmother of 8. I would never try to tell my children how to good spouses or tell my son and daughter in law how to be good spouses. I do give advice to them about my grandchildren, but realize that my advice might not be heeded. They have to make their own mistakes, just like I did. I never openly disagree with them in front of the children. The only time I would absolutely make a stand is if the children were in danger!!!!!!!
Mother-in-laws would constantly stay in their childrens' business, should get a life and stop living through their children.