How many of the members of the 104th corps are titan shifters? So far 


   Eren, Annie, and Ymir 


have been shown to be titan shifters. From an Attack on Titan wikia I know also


   Reiner and Bertolt are also titan shifters


How many more are known to be titan shifters from the manga? Are there more titan shifters than humans in that division?
Those are the only ones inside the walls.


   there are nine titan powers, Eren currently possesses the attack titan and the founder titan, Reiner has the armored titan, Berthold has the colossal titan and I don't know what is Ymis's titan. there is also a beast titan power that is in the Marleys hands and is said to possess the ability to change regular Eldians into mindless titans using his spinal fluid and then the beast titan is able to control them. and also Anne had the female titan and is now crystallized.