What should married children do regarding the mother who expelled their father from the home?

The husband's right over his wife is great, and it is forbidden for the wife to expel her husband from the house without just cause. You must advise her, remind her, and gently forbid her from injustice, for that is an act of righteousness. However, if her expulsion of him is justified (such as if the house belongs to her), then reconciliation between them is necessary, along with assisting them in solving their problems and advising them to fear Allah and for each to fulfill the rights of the other.