1. they will, given the right conditions
2. it would be best, or blue first, then yellow
3. a qt is used to "quarantine", not just hold, the fish. If your fish develop ich, or have any other disease, and you have them in the sump, they will infect the rest of your livestock.
is your tank size 3x1.5x2 feet? or meters? if it's feet, you proly shouldn't put the 2 tangs in it. (or, if they are small, just be aware of the fact that you might need to take them out at some point).