Players cannot attack members of their own alliance, members of alliances set to 'ally' by and officer or members of an alliance set to to 'NAP'. Red coloured and white coloured alliances and players as well as the forgotten are the only ones you're able to attack. I've played for 5 years and in that time it has never been possible to attack your own alliance members.
If a player won't move, for example because they haven't logged in for a long time, then it is up to an officer to remove them from the alliance.