A simple solution is this if you are the tank you inform the party. that "If you spank it, you tank it." and enforce that. so if that DPS goes crazy, you stand back and watch and if they die sucks to be them and don't rez them, if you play a healer same rule applies they spank it they tank it, with no heals.

Now as a tank if they refuse to attack the target you are I would inform the healer not to heal them since they refuse to help, only time the DPS should not attack the same target is when it goes after the healer. if you are using marks tell them that this symbol is target 1 this target is a sleep and save this mark target for last. if they refuse to do that then they are a remedial player and need to sloth their way back to WoW.