Fish problem!!!!!!!!!?

okay so i have this orange platy that i got form the pet store about 2 weeks ago. but lately its stomach is discolored like almost a yellowish brown and bigger than usual. i looked up these symptoms online and they all point to the fish being pregnant. i'm not sure if the fish got pregnant at the pet store or in my home aquarium, but i do not have any other platys in my home aquarium. I have mollies, serpae tetras, a cory, a neon tetra, and a black skirt tetra. could any of these species of fish interbreed with my platy? i'm not completely convinced though, and neither are my parents. my dad said he'll beleive the fish is pregnant when you see a bunch of little black dots on her stomach, which he says are the baby fish eyes. i'm not sure if this fact is true, but if it is it seems like the fish would have be very far along to be able to see the baby fishes eyes. the problem is, my dad won't buy the floating breeding tank until he is sure its pregnant. now i don't know alot about fish, but i know that they tend to eat their young, so i would not like the fish to give birth without the breeding tank. are there any tell-tale behavior or signs of pregnant orange platys that i can show him to convince him? i'm trying to figure out how to upload a video so you can make the judgement on whether or not the platy is pregnant.