@oristarA,
If the "mm" is used often and your party is known to be mostly girls I think it would work. The problem is that many people will think you've made a typo.
My only suggestion would be to make it obvious that you're misspelled the word on purpose: m.members, mm.members (those have kind of an internet flavor), mMembers, mmMembers.
I love new words! Good luck in getting it to catch on.