With mollies in small numbers, just like other livebearers in small numbers, it is best to keep 2 or 3 females for each male. Something else to consider when adding mollies is the water itself. Mollies do best in fairly hard, high pH water, not soft water and not a pH less than about 7.5. We do not know what your water is like so it is wreckless to say they would be OK in your water. Compatibility is not the issue here, but water parameters. All of your tetras would flourish in lower pH and softer water than a molly should ordinarily be put into. I have no idea on the shark but most of them deserve the name shark in terms of what they do to small fish.