What is the GH (general hardness), KH (carbonate hardness) and pH of your water supply?
This information can usually be obtained from your water supply company's website or by telephoning them. If they can't help you, take a glass full of tap water to the local pet shop and get them to test it for you. Write the results down (in numbers) when they do the tests. And ask them what the results are in (eg: ppm, dGH, or something else).
Mollies need water with a GH above 250ppm and a pH above 7.0.
Guppies need water with a GH above 200ppm and a pH above 7.0.
If the water is too soft or the pH gets too low, they will suffer.
The fish in the first picture are common mollies (Poecilia sphenops). You have a female black molly and a dalmation (black & white spotty one) molly. Not sure about the sex of the dalmation but it' probably a female.
The fish in the second picture is a male sailfin molly (Poecilia velifera or P. latipinna).