Do you know what your water hardness is?
According to seriouslyFish, mollies require water with hardness of at least 267 ppm, while the maximum hardness that neons can tolerate is 215 ppm. This means that neither the molly nor the tetra will be optimally happy in the same tank. That being said, both fish are heavily commercially bred and will likely tolerate water outside their genetically programmed habitat, but when deciding which fish to get more of, I'd probably recommend sticking with the fish that matches your water parameters.
As far as your sucking loach, it looks like a chinese algae eater potentially? I am not an expert so I might have that wrong.
These are the seriouslyfish profiles for your fish, you can look at these pages to determine the water parameters and other needs of the fish (use an online calculator to convert from dH to ppm, since not all profiles report hardness in the same units):
www.seriouslyfish.com
www.seriouslyfish.com
www.seriouslyfish.com