Common is meant to cover everyone who isn't royalty or nobility. I don't use either term in a derogatory way.
That's "commoner". It is a technical term, it just means "not noble or royal" and carries no implication of uncouthness or ill-breeding. I don't think you got the point I made about my mother. "Common" is a word used by petit-bourgeois and upper working class people about those they see as "below" them. It is rapidly dying out.
Incidentally, a good way to wind up Americans is to pull their chains about class, e.g. "I couldn't go out with Mary; she's too common." Never fails.