.. Where did all these people come from?

That's a good question, and it's going to be quite difficult to get a straight answer from any of them.

The two people who suddenly appeared when you lit up the burial chamber are Dylan, who spends all his time sitting next to the water truck, and Jamila, who you can initially find at the end of tunnel 2. After you ask Abdullah about her --

-- she'll move to the big room in tunnel 3, and she'll be there for the rest of the game.

Go talk to both of them and see what you can figure out, then go talk to Lily and Abdullah about them.

You won't find out a lot, but it might make you feel less uncomfortable.