We know broadside songs were sung, because the street sellers sang them.
Not necessarily true Jack
Broadside expert Leslie Shepherd suggested that many of them were never sung

So what? Most of the ones we know about were, because the sellers sang them to get sales, and it was the ones that sold that ended up in libraries. The sales pitch was described by John Gay in a piece I quoted a few weeks ago, and much later (in grim detail) by Henry Mayhew.

Typically a song sheet had three songs on it, and the seller wouldn't have sung all of them, but they would have done the headline number.