You can access to Naxxanar (where the 3 elites are) from Temple of En'kilah. Enter the temple and turn right, there's an orb to use and then a portal to enter right after.
First floor [ Luthion and Vanthryn ]
When you're inside Naxxanar there are some necro who cast fireball/frostbolt (easy non elite mobs), clear the ones you need to get to Luthion and Vanthryn who are in this floor. They are both melees and they hit around 800/900 on me (moonkin with 15k armor) but they are definitely snarable so shouldn't be a problem for most classes to solo.
Second floor [ Prince Valanar ]
When you're finished with them, go where you got ported but just 2 yards up (remember Naxxramas?) and go to the next floor of Naxxanar. There's some deathblade on your way to Prince Valanar but they are easy non elite mobs, clear them and get to him. Valanar casts 2.3k shadowbolts and he hits on me (moonkin with 15k armor) around 1300/1400. You can avoid shadowbolts just using line of sight. If you're a healer this is the easiest of the three elites since you can just heal up the bolts and keep up the dps all the time. As stated above, if you have bt shadow resist gear you should take him down without any problems at all.
As a moonkin I soloed them easily, dunno about melees like wars and rogues or priests. For wars and rogues, you can probably nuke them down using a couple of cooldowns or you can just snare the first two, go out of los and bandage if you need.
If you wanna go easy bring someone with you. This should be the last quest of Taunka'le.