I did this same quest. After talking to Paul and finding that things got a bit hairy if I brought him along, decided to talk to Henry the bartender alone and convince him to ban Paul's wife from the bar. I went with Henry to the chems deal, yeah they didn't give me a good transition to that part either. I bombed the chems deal, literally, with artillery fire. Somehow Henry survived and I spoke to him after everyone else at the deal was already dead, then he decided to shuffle off. He must have gotten into some trouble afterwards as his daughter tracked me down in Diamond City later and accused me of killing her father Henry. The next time I see him, Paul Pembroke says something to the effect of "Now what can you do to ruin my life more than you have?".
Long story short, too many bugs involved for this quest to go smoothly. Nothing makes sense. No one is happy but me... ah... sweet therapeutic artillery fire.