For starters, if only 1 out of 6 mollys is female, then you'll surely want to either get rid of her or seperate her from the males. 1 female with a group of 5 males is an early death for that female. The males will exhaust her to death trying to breed. In the future, when keeping livebearing fish, the ratio should be 2 or more females for each male.
Not all pet stores will take fish back... and while some may take them, they often don't offer any money for them. The only thing we can suggest there is to call and ask.
Your new stocking idea should work out just fine provided it has plenty of decorations to help break up territory and allow the glass cats a lot of hiding places. Glass cats stress very very easy, and that is one reason they can be difficult to keep. They also prefer a larger school of their own kind, although I have seen it work with 3 - 5 of them in a tank, provided they have no predators with them and water params are good, stress is accounted for, etc.
If you wish to go with that stocking idea, my suggestion would be to start with the glass cats, then allow 2 - 3 wks before adding the hatchet fish, and then finally the shrimp a few wks later. By breaking up the additions with a 2 - 3 wk gap between species, this will avoid overwhelming waste levels that would wipe out everything if they are added all at once.
The only other fish I can think other than a species of hatchet you're thinking of, would be indian glass fish... and those I would not mix with glass cats. You might want to try black wing hatchet fish, who have more of a transparent appearance than most other hatchets... they stay small and are peaceful. Indian glass fish can get a bit nippy, and they would require the same territory as the glass cats, which could cause a conflict. Both of those types of fish are mid dwelling. The black wing hatchets are upper level, which resolves most conflict issues right there.