Are Al-Qahtani, Al-Mansour, Al-Yamani, and Al-Mahdi the same person?

Al-Qahtani and Al-Mahdi are not the same person. Al-Mahdi is from the progeny of the Prophet, may Allah bless him and grant him peace. His reign will last seven years, and his name is Muhammad ibn Abdullah. Al-Qahtani is a man from Qahtan, his reign will last twenty years, and his name is Jahjah. He will appear after Al-Mahdi, indeed, even after Dhul-Suwayqatayn.