Hey, those girls did a great job of including their little friend in alternate play. We make concessions, compromises and change plans all the time. I don't think it's that big a deal. Sometimes the others will be happy to change, sometimes that kid will miss out on stuff. But it's probably much the same for everybody at one time or another.
anyway, I reckon it's good the girls just figured it out for themselves.
I dunno about you always hosting the other kids, though. You ok with that?