How can I help my 21-year-old son and his 80-year-old grandparents get along?

To launch himself into adulthood, my son moved to the mainland. He’s staying with my parents. He’s already found a job, which won’t start for another two weeks.

In the meantime, the two generations are not getting along well. One feels disrespected, and the other feels unheard.

What can I do to help?

I’ve told my son that I’ll talk to my mother, and I’ve strongly suggested he approach them with specific ways he can be supportive around their house.