The MOST important thing in any marriage is the marriage itself and no one should allow ANYONE to interfere with it. So no man nor woman should allow either mother or father to interfere between husband and wife. That is rule number one!
A husband’s first priority is his wife not his mother. A wife’s first priority is her husband.
Having said that both the husband and the wife have the obligation of kibud av v’em to both sets of parents. And that should be done as a couple and not as a disjointed group. It is up to the husband to make his parents understand that his wife is his top priority and it is up to the wife to make her parents understand that her husband is her top priority. It is up to each spouse to make the other understand that their families are very important to them and that they want everyone to get along harmoniously.
IMHO, it is up to the mothers-in-law to lay the foundation of a secure and safe relationship. It may not always work, but they have the upper hand and therefore it is easier for them to lay the groundwork for a warm, loving and caring relationship with their in-law children. It does not happen overnight, it does take time to build up, but if you start off on the right footing it should give you the opportunity to head down the right path.