Yes. A secondary attack is a separate attack from the primary attack.
Do you have a reference or cite for this? I'm not disputing your answer, but it seems a bit counterintuitive if it is part of the same power.
Now, say I target two creatures with twin strike instead?
[I'm pretty strongly of the opinion that this is just a gray area in the rules, and can be addressed by the DM as such]

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.