I would just leave them to it and they will sort out who is allowed where between themselves!

Mickey and Mazie 'allow' certain cats into our garden but chase others away, it is quite funny to watch. Mickey has had a few scraps but nothing major and the other cat normally runs away and Mickey runs inside!

I should also add that Mickey is more friendly with the other cats and runs off with them leaving Mazie but I think Mazie is more independent and entertains herself. Unfortunately you can't make them play nicely together like children!!