Hi Laish,
The answer to that is, one of the future popes is not going to be the antichrist, but the false prophet. This can easily be deduced by comparing the second beast in Rev.13 with the false prophet mentioned in Rev.16. What links them together as being the same person is that, they are both said to be that one who performs the miracles, signs and wonders in order to deceive people. The "false prophet" is just another designation for that second beast.
Also, regarding Islam, they do not fit the criteria of being the false prophet and that because that designation refers to someone who is disobeying Christ while claiming to be his true follower. Islam is not proclaiming to be of Christ, but is just a pagan religious system, just as is Buddhism or Hinduism, just to name a few. Roman Catholicism on the other hand, fits the characteristics in Revelation to a tee. The RCC is proclaiming to be of Christ, but she is Mystery, Babylon the great! Most of her characteristics, her practices and rituals, stem from the mystery religions of Babylon, such as queen of heaven and mother and son worship. Out in the middle of St. Peter's square stands an 82 ft. Egyptian obelisk, which is pagan in origin and definitely not something that God would approve of.
Just a cursory look at the RCC and it becomes obvious that she is a counterfeit church. And when that antichrist is revealed, he is going to provide the power that she and her pope's once wielded against kings and their armies. She thinks that she is the true church and that everyone should come under the authority of the pope. And during those days, anyone who rejects the beast, his image or his mark will be enemies of both the beast and the false prophet with the consequences being persecution and death.
"The woman you saw is that great city who rules over the kings of the earth"
At the time that John was receiving that information, Rome was that great city that ruled over the kings of the earth.
"The seven heads are seven hills/mountains upon which the woman sits."
Rome was literally built on and is famous for her seven hills."