Hello! I see you have green spotted puffers! Puffers are my passion! I expect pics of them shortly, lol.

I don't know if you've found the answer to your molly question yet... but the males will have a rod-like anal fin called a
gonopodium, and the females will be a bit chunkier and have rounded anal fins.
May I ask what kind of pleco you have? Most of them are actually intolerant of salt, and will not do well in your brackish aquarium (if it is indeed in your brackish and I am not mistaken)
Glad you joined!