You need a burglar to do this.
To get past the trash mobs
before the first boss, have the burglar drop the group and run to the
hallway just before the 1st boss. The burglar will just train all of
the trash. The group follows, and then when you get to the hallway, the
burglar will hid to lose aggro. Reinvite the burglar. After the 1st
boss, you can repeat this to get to the 2nd boss. The burglar can also
use stealth to turn the wheels and open the gate to the 2nd boss. After
the 2nd boss, just run to the fungal queens and kill them. Go to the
final boss and kill it.
To get past the trash mobs
before the first boss, have the burglar drop the group and run to the
hallway just before the 1st boss. The burglar will just train all of
the trash. The group follows, and then when you get to the hallway, the
burglar will hid to lose aggro. Reinvite the burglar. After the 1st
boss, you can repeat this to get to the 2nd boss. The burglar can also
use stealth to turn the wheels and open the gate to the 2nd boss. After
the 2nd boss, just run to the fungal queens and kill them. Go to the
final boss and kill it.