Talk to Morgan each night and when you see him in the nightmare on landings. He's the guy with the police outfit sitting in the lower-left corner of the booths. He will be there on:
Day 3 from 21:15 to 22:00. Kind of the middle of the night. Once you see Daniel and Anna leave (the couple) talk to him right away, as he doesn't have much longer.
Day 4 from opening to 21:00. He's the next person to leave after the creepy twins, so he should be the first person you talk to that night.
Day 5 from 21:25 to 22:20. He enters about halfway through the night, and will leave at last call right before Catherine comes in. Once Justin (the reporter) leaves, Morgan will be leaving next. Answer to his question: "If I have to choose, yes."
Day 8 from 21:00 'til closing time. You can't miss this one, as you are allowed to linger as long as you desire.
You also need to talk to him each time you see him on the landing during the nightmares (he won't show up until the 4th level). He is the "Sheep with Police Hat". Just be encouraging here; the answers should be obvious. But let me know if there's one you aren't sure about.
NOTE: I am 99% certain I gave a "wrong" answer or two at the Stray Sheep, according to the wiki, and still popped all the helper achievements. I include the answers so that you can be on the safe side, but you may very well be able to answer however you like. If you have confirmation of this, please comment. If you want to be safe, answer as posted above.