During even the best of times, relations with extended family can be challenging to navigate. These challenges may compound and manifest in many different ways during the process of separation or divorce.
Depending on the type of relationships you and your spouse have with your respective families, it is quite possible that the divorce or separation may come as a surprise to many in your extended families. It is important to be as level headed in the beginning. Inevitably extended family picks sides, even unintentionally, and you want to do everything you can to avoid adding fuel to the fire of your already complex situation.
Grandparents can be a wonderful support system for both parents and children during a divorce but it is important to maintain clearly defined boundaries that are mutually respected. Grandparents are likely to have many of their own unique emotional reactions to divorce or separation that often involve the desire to protect their own child as well as their grandchildren. This behavior is often incredibly counterproductive and actually damages children emotionally if they are made to feel like their grandparents have sided with one parent over the other.
This being said, if your nuclear family is accustomed to close relations with extended family, it is necessary for you to attempt to maintain those for your children. Even the most amicable of divorces is difficult for children and the additional disruption of having other family ties severed only worsens the effects. Should you be required to continue to accept unsolicited parenting advice from your mother in law? No. However, fostering that relationship between her and your children is important.