lots of men are not interested in socializing with their in-laws for one reason or another. at least he respects you this much that he just goes to another room instead of fighting with them or making faces in front of them to make it obvious. some men aer way worse than your husband. anyways isn't it a person's own choice who they want to talk to and who dont want to be chummy with?
they probably do or say something to make him feel uncomfortable but you don't realize it or they don't do it in front of you. this is what a lot of bahoos have to put up with. in this case it is the damad.