So who are the Two Witnesses?

Elijah and Moses.

"3And I will give power to my two witnesses"

"they will prophesy for 1,260 days, clothed in sackcloth."

"4These are the two olive trees and the two lampstands that stand before the Lord of the earth."

"6These men have power to shut up the sky so that it will not rain during the time they are prophesying;" - Elijah

"they have power to turn the waters into blood and to strike the earth with every kind of plague as often as they want." - Moses