Originally Posted by Mornai
They may still join you even if you don't reveal your bite. I think it has to do with the final ep. 3 choice, "Did you help Omid?". If you helped him, they join you but if you didn't help him, they'll stay behind. Not entirely sure on that but why else would it be one of the 5 major decisions?
I'm pretty sure it doesn't matter who you saved first. On my first playthrough, I didn't reveal my bite to them and I went with Ben. When we came back, I told them that I was bitten and she said that they would a joined me if I had told them I was bitten right after I got bit.