My mother-in-law is gone, and my father-in-law occasionally wears underwear in front of her husband when he comes back from work in summer. Is this appropriate?

This is inappropriate. After all, you are the father-in-law. There is also a daughter-in-law at home. Right in front of my son. It's not appropriate to be an elder. You should. Respect yourself. It is also a respect for others. My father-in-law and my mother-in-law are just different. My mother-in-law left. Grandpa should pay more attention. You can buy a pair of bigger shorts to wear. So young people are willing to live alone. With the old man. It's really inconvenient for the elderly to think more about their children. It's gonna be okay.