With regard to the two witnesses discussed in Revelation 11, I’ve heard, and even believed myself, it will most likely be a combination of Moses and either Elijah or Enoch. However, I got to pondering the rapture of Elijah and Enoch and realized, no one can enter heaven without first exchanging the corruptible for the incorruptible and mortal into immortality. Since Elijah and Enoch both would have been transformed before entering heaven, they would be immortal, and therefore, not be able to be killed by the anti-Christ during the tribulation. Could it possibly be that the two witnesses spoken of are merely men God will raise up during that time?
These two witnesses will need to be credible in Israel. I believe performing the miracles identified with Moses and Elijah as they do is meant to provide this. They may not be in the actual bodies that Moses and Elijah originally inhabited, but I believe they will be thought of as these two men. And remember, Elijah has already come back once as John the Baptist and was killed by King Herod, (Matt. 17:10-13) so this kind of thing is possible with God.