My husband and I put a very prompt stop to my mother's attempts to interefere in our marriage, which she felt perfectly entitled to do. Much as I loved her, I was not prepared to let my mother tell me how to live my life.
My mother-in-law had sadly died before my husband and I married. I doubt she would have tried to interfere, as I have always understood that she resembled my elder sister-in-law, and neither of my husband's sisters have try to interfere.
Reading the posts on gransnet I often get the feeling that the in-law relationship is hard, especially in the UK, but presumably we only hear about the relationships that are not working well on Gransnet.