Your molly looks pregnant to me.
The best piece of advice i can offer you is to learn/force yourself to live within your means as a fish keeper.
Right now you may have just enough swimming room in your tank and you can compensate for the larger than necessary bioload of your tank by doing more frequent partial water changes, but when your molly gives birth your tank will be overcrowded if any of those babies survive.
This is something i struggle with myself. I have guppies and the saying goes, "if you have guppies, you have pregnant guppies". I can't justify buying a new tank every month, so i end up feeding newly born fry to my
betta fishes and raising the rest to give to my friend who has a Jack Dempsy while saving a few of the best specimens to keep for myself.