What are my duties towards my father-in-law who suffers from Alzheimer's and whose presence causes problems and tension?

A wife is not obligated to serve her husband's parents or relatives. Rather, it falls under the category of chivalry and good treatment. It is not permissible for the husband to compel her to do so. It is advisable for the wife to be patient in this matter, as it increases her honor and affection in the eyes of her husband.