Help! 2 sunset platys, one might be preg?

[milogen]

I recently got 2 sunset platys and I originally thought they were both boys. Especially since the bigger one chased the littler one around a lot (it doesnt do that anymore though, for some reason. Maybe they worked it out?). But after some research apparently, the girls have rounder, fan-shaped fins near their bums. I can't really place what sex these two are anymore, and I have a suspicion that the bigger one might be a female and pregnant. I need to know, what sexes are these two and am I right about the pregnancy??
Sorry for bad lighting in the first pic. I tried.

 

[NickAu]

The top one in the right photo is a female. And its safe to assume that all female live bearers are pregnant when you buy them.