Is a wife's service to her husband's parents obligatory, and what are the consequences of that?

The wife's service to her husband's parents is not obligatory upon her. If she does so voluntarily, she will be rewarded. There is no blame upon the husband if he asks her to do so, or if he marries her with this intention, as Jabir (may Allah be pleased with him) did when he married a previously married woman to take care of his sisters. Although this service is not obligatory, refraining from being kind to them is not part of living together honorably. If the wife refuses to serve, the husband himself should serve his parents.