1. When Lydia pulled the fire alarm, what was that supposed to accomplish?
2. Which twin took off her hijab at the end? Nimah or Raina? And what was the significance of that and the other twin being held hostage in the next room?
1) She pulled the firearms to alert the terrorists. She has handcuffed (or tied?) Alex in the room for her to be found by the terrorists. Also, when they find the hard drives missing, she can begin the bargain.
2) It was Nimah. She doesn't wear a hijab and her twin Raina does. She took off the hijab so that we know it was Nimah pretending to be Raina. Raina was held in the other room to show that she is actually innocent and really wanted to help Alex. Also, since Nimah is helping Ryan and Alex at The Farm in the flashback, so she is ditching them