Yagorath is the largest target in the game. You can shoot your Fire Spit and let it hit her directly for a significant damage boost. If you combine it with the Fusillade talent, your rockets will be able to overpower her natural damage reduction.
When Vivian's ult is up, combo your Fire Spit and Salvo on her. The AoE damage will seriously hurt her and her ult drones, if not outright kill. If you can't get close enough, poke her from a distance.
Be very careful of Khan ult, as if Inara gets thrown off the map, she has no way to save herself. You can use the Mother's Grace talent to give him fewer chances to attempt to grab you, otherwise play carefully with lines of sight.