Suggestion is that if a player has family members or close friends on this site, that they have a thing that displays on their wall or profile which fully discloses this relationship to potential opponents.
I see a number of folks who get called for being mutlis and secret diplomacy, and then try to excuse that by saying "those are my kids, or that is my girlfriend, or husband, or whatever". Best to state that straight up so players have a chance of knowing what they may be getting into.
Maybe a way to flag games that have family/friends together in them would also be helpful.
That way if a multi gets called out, they cannot so readily fall back on this excuse.