When it's obvious that there are way more members of one faction than another conquering the core other factions should be able to team up (officially) and not kill each other, it takes an impossible amount of cooperation if you are trying to cooperate with another faction, but if they officially joined ( or as I suggested before have a neutral faction that can join the weakest faction in battle)
When one faction has 10 members, and the 2nd faction has 8 members and the other 2 factions have 1 person online it is just said, and demotes PVP.