One way to kill Batraal (Dzemael Darkhold)

[Corrderio]

One is like a circle blade where he spins around.
one is a backflip and he poisons you
one is a multiple slash
and a wide area directional laser beam type thing.

the only person in range of these is your tank. the healer and DD's stay in safe spots noted on diagram

What should the DDs do then? Seems like they're not doing anything in the safe zone.