Apparently Hassani is a follower of Sadar.
No. Hassani is a follower of Sadar's dad. He would be considered a rival to Sadar.
Al Yamani is another name for Ahmed bin al Hassan who was a student of Ayatollah Mohammed al Sadr, the Shia cleric slain in 1999 and the father of Muqtada al Sadr. About two years ago al Yamani began calling on people to follow him and claiming that he had seen Imam al Mahdi (the twelfth Shia Imam who went into occultation in the 10th century AD and is expected to return like the messiah) and that the Mahdi had ordered him to lead the nation. He sent letters to presidents and leaders (including Bush in the U.S. and Khamenai in Iran ) asking them to leave power and submit to his orders. Until recently his movement was quiet and it was ignored by Shia and the authorities.