I keep mollys and three of them are in a 100L tank...I wouldn't put them in anything smaller than a 60L. Your 25L tank is just way way way too small for mollys, plus they require salt to remain healthy and you can make serious mistakes with a 25L and salt addition if you are not careful.
I'd go for a betta if I were you or some small fish. When mollys have fry they really have fry!! You may find yourself dangerously overstocked when a female has a batch of fry one morning!!
And remember if you are getting females there is a high chance that they have already mated with a male in the pet store and will give birth to fry for the following 6 to 8 months without a male in the tank with her. If you want to avoid getting fry you can only go for 1 male...if you get 2 males they will fight, mine did and I had to buy a tank just to seperate them!!!
Do yourself and the fish a favour and reconsider the fish you are going to get, its not nice to look at an overstocked tank that is not relaxing, and this also hightens the chances of disease breaking out.