Same mom, same litter, different dads?

My feral turned indoor cat (against her will) popped out 4 kittens. One is definitely a short hair torbie that looks exactly like mom and the other three are orange, black, and another female torbie. The three fluff balls look Persian and their sister, which is the runt of the litter, looks nothing like them. Please help me understand why the three fluff balls look alike and the other one is very obviously the odd girl out.