I agree sometimes it's a real trouble, but If people can't be able to follow the rules of their kingdom or can't respect each other , this has nothing to do with the construction of the game.
In my opinion leaders and players have to solve "internal wars" as an internal issue, that's why Travian is a strategical game.
On the other hand an "internal competition" between the players is not so bad in case it's based on the kingdom's rules..
i don't know how it can be done but i was wondering :
if both kings could have access to the camp's rally point watching the process of cleaning the camps...then what?