That's why I specified daytime vs nighttime visitors. It's definitely possible to have Celeste + someone or Wisp + someone. Also, I sometimes have Sunday overlap with Daisy Mae, thus why I didn't mention her (I've got Leif + Daisy Mae right now).
I've never seen a plaza + other wandering one at the same time though. For example, Saharah + Kicks or Leif + Flick. I don't know if those things are possible or not. I haven't seen it yet, anyway.