You need to break autofollow and tank with 1 horse, charge with the other 4( a 2nd autofollow key is handy here, one that only includes your 4 shamans, not your tank ). Autofollow is not your friend here, you should have 4 horses constantly charging the mobs while 1 horse tanks, your "tank" will change often due to the amount of dmg the chargers do. If you absolutely can't handle changing mains rapidly then you could probably kite them around with autofollow like your doing but at the very least your followers could be doing a lot more thrusting from what I see in this video, their doing nada 90% of the fight while you try to solo it with 1 dude.