As they're female platys, the chances that they are pregnant are high. But they don't look like they're about to have babies soon from what I can see. I'd suggest that you get some java moss (you can get it on the internet if your local shop doesn't have any), and dump it in the tank. Leave your platys in there, and just keep an eye on things. The more hiding places the better, for mother and babies. Almost certainly a few of the babies will survive in the moss, and that will help you to get an idea of what the female will look like when she's about to give birth, plus you won't get too over-run with babies.
We've had platys for about 3 months now, and just got our 3rd batch of babies. Only 1 survived from the first batch, but that was before I got the java moss - I thought they'd all been eaten, but about 2 weeks later, he suddenly appeared from under some bogwood. There are 3 growing on from the second batch, and I've counted at least 5 from the third. I just feed as normal, but make sure some crushed up flake, freeze-dried brine shrimp, or a bit of tablet falls into the moss. I've got a friend who'll hopefully take some of them when they're a bit bigger, but couldn't cope with many more!
I agree, those white MMs are gorgeous!