So me and my brother was in Blightfire moors in the Drinal Server and for some reason his merc wouldn't move at all he tried changing his merc and that didn't help. the merc just always sits right where you spawn in blightfire. What can he do to fix it?
The most common reason for this behavior is that the player is marked as puller. The whole point of that group role is to prevent the mercenary from following the player (generally speaking, it starts to follow someone else in the group). Depending on your scenario, if you/your brother are parked on a hillside, that can cause some pathing issues as well. If you provide more details, others may be able to provide better assistance.
Is the merc a healer or a tank or a caster? Is it set to passive or aggressive? Does the merc react correctly in other zones like Cresent Reach?