Talus is a good champion to flank Dredge. Talus can disrupt Dredges flow of dealing damage and stop him from spamming his AoE (Area of Effect) attacks. Talus should kill him if he can but teleporting back to his portal is still ok as you dealt damage
When u hear the Kinetic Burst sound or see the animation, use your shield to tank the next hit.
For her dash use Commander's Grab, that has a bigger hitbox, in the direction she is looking.
And when she ults, use your ultimate to take her out.
Maeve is probably the safest pick against Raum, cause its hard for him to hit you. He also has high damage-falloff, you don't, so you can use that to your advantage and keep your distance.