P.51 Music Men have names, but do you know them?

Give it a try in the comments. First names only. What song were they playing?
The man at the piano is what relation to Clair?

The one standing is Jon, his dad, Joe is at the piano, Scott (Lindy's son) is playing the sax. Joe is Uncle Clair's nephew, just as you are - we are all the #3 generation - Uncle Clair is #2