Who is the mother of baby fry?

Who is the mother? Please read this and help me find out!

First balloon female-

She was the first fish I got for my tank along with others. Her and this black male mated like crazy, and she always had a bulge around her belly. Today, some baby fry were born. I didn't see the birth, but found the last remaining babies in the tank and saved them. I think that she could be the mother, but there are two more females that it could be. One is bright white, and the baby fry are dark brown, so I konw it can't be her. The other one is dark brown, and a regular molly. If she is the mother, the black male can be the daddy because he has never mated with her before. There is another male in the tank, but he NEVER mates with anyone. So, if the regular molly is the mother, she would of had to of got pregnant in the store with the other males in her tank. When I first bought her, she was quite plump. But then again, it could be the balloon molly that is the mother, because after the baby fry were born she had no bulge. Who is the mother? It totally confuses me!

I'll try my best to find out, but at the end of the day what really matters is that the babies are safe and well. If my mollies keep on having more and more babies in the future, and I have no room for them, can I take them back to the store and ask the store if they can look after them?(and sell them, of course).