1. You are correct. however, if someone has Double-Barrel, they will inflict one damage.
2. Yes and No. The Double-Barrel is a modification to your "Main Laser". So options like Scrambler would still only have one shot.
Regarding Fire Control, it is also a Main Laser modification, so you can use both.
From the faq:
Q: When using a double-barrelled-laser, what are the targetting options?
A: It is treated as two different shots, but they must both be to the same area. (i.e.: You may cause two points of damage, target two options, or target any two registers.) If not treated as two separate shots, then it is no different from the high-powered-laser.