I recently decided I was going to GM a PF campaign set in the drow underdark. The PC's were all pretty excited at the concept and I got to work.

Being fairly new to the entire system, I decided I'd have a little test run of everyone's characters, and also having the encounter be the reason they come together. I admit, I wrongly gave them an enemy that was far above their skill level, but I provided meat shields just in case to help with the fight.

Combat went great. It was in detail, our Tiefling really put out the DPS, and it seemed like everyone enjoyed that much. But then I had to act as NPC's. And goddammit, I suck at it. It's not that I can't act, usually I can get into character fine, it's just coming up with acceptable dialogue that actually makes sense is my worst subject.

To put things in perspective, the party consists of a Dhampir Slayer, a Tiefling Bloodrager, a Half-Drow Vivisectionist, a Dwarf Gunslinger, and a Human Swashbuckler. They are all slaves to certain drow nobles and priestesses and matriarchs respectively.

The first three fit the story amazingly, their backstories intertwined in a way that made sense. But the Dwarfs just doesn't, and I tried to convince him to play something else but he insisted on being a dwarf. So I let him go with the idea that his Master just likes his skills with a gun, and bought him as his personal assassin. Which makes zero sense. Why would he need a dwarf gunslinger for anything? But the player insisted, and now my dialogue relating to his character comes off as strange and sheepish. The human is an entirely different subject, as his backstory makes some sense, but it's far too damn hard to incorporate it without setting the party off as 'this guy isn't one of us.' So I have the same problem with him.

I'm not sure what to do. I want all the players to enjoy a game I'm still learning the mechanics of, and most of them are Pathfinder adepts, but some of them aren't working with me and making the story come together is proving to be really difficult. Any help would be appreciated.