The final boss on Mandolorian Raiders, like most bosses, have an attack that randomly hits someone with no respect to aggro list. People usually panic too much when they see the boss randomly turn around to attack someone, not realizing that this is completely intended. On that boss if you AE at where the boss is, that will usually cover all the turrets. However due to the significant healing required, AE alone isn't going to hold aggro on the turret your tank isn't attacking. What I usually do is switch to the other turret about 10 seconds into the fight to make sure I have aggro on it, and DPS can just tank the other turret with CD if needed. You don't want the second turret to start hitting your healer, as that's very bad news. DPS should be able to tank one just fine with their CDs, and taunt should definitely be back up after the DPS's defensive CD runs out.
This is probably the worst way to go about getting both turrets. Unless the DPS are split between the turrets like idiots (this happens so often amongst pugs that it has become one of my primary sources of irritation), every tank should be able to maintain threat on *both* turrets at all times. It's actually pretty simple.
When the boss leaps away, while the turrets are spawning, thrown down a couple of AoEs on him; Slow Time and Force Breach will both cleave to the turrets, Guardian Slash and Force Sweep should as well, Pulse Cannon and the HiB cleave will do the job (Mortar Volley should be able to as well). If you're a Guardian, just throw save Saber Reflect for when the Turrets have popped up and you'll have all the threat you'll ever need on them (9k from Saber Reflect itself and then even more from the actual reflected damage since ranged attacks are *all* the turrets do). Once you've used your 2-3 consecutive AoE casts, swap over to the turret that the DPS are going to focus on. Whenever your AoE comes up again, you can either use it on the turret so that the other turret isn't caught in it or you can swap over to the boss and make sure all 3 are caught in it. AoE damage is only taboo in that fight when DPS are dropping it. Tank AoEs don't hit hard enough to actually cause Mavrix to swap over soon enough, so it's not going to be a concern.
Healer threat, on the other hand, is a complete joke, as it has always been. If the second turret *does* swap over to the healer before the first turret is dead, just swap targets to the second turret for half of a second, throw your taunt, and resume beating on the first turret. Healer threat is both diminished (50% base and often 35-40% after talents) and distributed (so if there are 3 NPCs in combat, all 3 get 33% of the total threat generated from a heal; if there are 5, all 5 get 20% of the total threat generated from a heal). Since there are 3 targets there, it's almost *impossible* for the turrets to swap to the healer if the tank has paid even the *smallest* amount of attention to them.