"should people who visit have someone approve their repertoire?" Nobody has suggested that "don't sing that song, it's Jenny's party piece" should apply to visitors, Repeatedly people posting here have said specifically that it shouldn't be expected to.

As for regulars, there are no hard and fast rules governing this kind of thing, and nor should there be. Just an expectation that people will judge what good manners requires. Most people can manage that. In fact in this context in my experience, most people do.