0.999999999c
Yes, barring the fact their ship would be annihilated, their bodies faring no better, and the incredible amounts of energy required to go that fast.

Well, to nitpick, photons aren't "energy", they're massless particles. Matter isn't any more or less made of energy than photons are. You can't reach the speed of light unless you're massless, though, that's correct.
Stop nitpicking. It's irrelevant. (In other words, you're making me feel stupid and forgetful. )