Parabalus only one advice in general, your companions are great at taking damage, just give them pistols & shields, they will do more than enough damage and give your PC time to take down the most important targets.
The other important thing is: You can maintain your left-click on companions to give them order, thus, at a certain point, they almost can't die, as soon as you feel that they are in danger, tell them to ''avoid'', and they will run out of combat.
Companions are really priceless, they can deal damage, take a ton and transport your stuff.
If you want to heal them, the best thing to do is to eat & rest.
If you feel that they are using too much ammo, just order them to not use firearms during a specific fight.
Red Fighter is really costly to upgrade, I am not very certain it is worth it, but the fact that you can craft 9mm ammo so easy thanks for the armory upgrade is certainly something you want to take into account for your companions.
Pistol, is the key: No burst: thus they don't kill your PC, 1 hand, thus they can pick shield, and low cost ammo.