What you need to control your sessions is a good "fear a' ti" - man of the house. Irish music sessions or ceili (in irish) originated when groups in local communities came together in one house for mutual entertainment. The most successful sessions depended on a good fear an ti whose main job was to control the politics of the session. He would know when to call for a song or a particular singer. He would know if there was a very good singer or musician lurking in the shadows but too shy to come forward. He didn't try to totally control events but to gently move the session in a certain direction.
The fear an ti was often not a musician as they are too involved in the music to suss out whats going on in the room but he would probably have a song or two - or a story to tell.

If you need to control your session get yourself a good fear a'ti or bean a' ti (woman of the house.