My LMP was 02/March/13 and had with A on the 09/March/2013 and with B on the 23/March 2013. Both ejaculated outside. And I went for my sonar and my due date is 03/12/2013...

Who could be the father of my baby.

Could be either as Gestational Dating is all based on Best Guess.
The ONLY surefire method is a DNA paternity test after the birth