ruckus doesn't have a shield in front of him that protects from stuns, so use your reload to deal with him. just avoid his high burst damage before you stun him, after that he has to spin his weapon for a second to get it back again.
Maeve struggles against groups of enemies, so stick close to your team, especially if you are a support, because you can pressure her either fight, where she will most likely lose, or to flee.
Koga can avoid Luna's stun so your best tool to handle him is to use Luna's large hitbox and healthpool to face tank his fire while taking chances to fire at him.