I have never had a problem with the kill quests in south icecrown. I use bindpad and have a macro that makes the leader the focus..switches my screen..follows and assists the focus.

so i use F4-F8 keys for PiP and making leader focus,assist and follow. It works with any vehicle i use ( jousting mounts and siege )
Bind Pad macors look like this ( simple as it can get )

/focus Whitelyon ( example )
/follow focus
/assist focus

This works for everything, including the tournament ground jousts. However, even though they follow and assist on the grounds, only the character that starts the joust can attack the npc.. if all are mounted. I now just have the slaves stay put, off the mounts, and attack normally. Works great.. i kill everything super fast! Also, for kicks, i put out my Fire eles and they help anyone who is jousting kill their npcs lol.. fun!