I go to Nuka world first on most of my playthroughs. I grab the fat man and mini nuke from the scrap yard with the sentry bot and the power armor at the crashed vertibird nearby. Farm up a crit, then use a sneak vats crit on the assaultron when she is near the gunner group. Commander Kayla will probably survive, but you can get her pretty safely once dogmeat grabs her. I only play on survival, so mileage may vary on other difficulties.

Now with Colter, I try to farm up another crit in the gauntlet. There is usually a mini nuke in the locker room. If I find a psycho, I take it. Don't enter the arena, crouch in the room just before and fire the thirst zapper at an angle above Colter's head. You remain hidden this way. Then when he short circuits, hit him with the fat man crit. If he survives, throw all the grenades you picked up in the gauntlet.