The First day of my last period was on the 20th of April 2013, I had intercourse on the 26th/27th of April, Than again on the 11th of May with two different guys, I am 12 days late, and have tested positive, But am confused to who the father could be, my period was due on the 18th of May, Can someone please help me figure who the father is ? And far along I am.

Seriously the dates are too close to even guess.
You will have to wait for the birth and use a DNA test to define paternity.