My mollies that I have had for about 7 months now just had some babbies 5 days ago. to tell if the females are pregnant, check if there is a darker area around their anus. it sounds gross, but if it is darker around there, those are probably the eggs developing. About 3 weeks after you see that area, move the female into a breeding trap or make shure you have some places for the fry to hide in your tank. I use java moss and it works great. about a week after you move her into the breeding trap (or 4 weeks after you see the dark spot, raise your tempertaure in your tank 2 degrees F. for a day or so. This will prompt the mollie to give birth.
if you have no places for the fry to hide in your tank, your other fish will eat them as soon as they see them.