Ok first off what all fish will play with toys or atleast show interest in them, Second How exactly does an oscar play with a ping pong ball, and third ok my cousin has had 2 oscars that were bought the same size and only like a month apart now they or like 2 years old and if one oscar gets to far from the other it will swim backwards till it can touch the other one again and they are very peaceful together so does this mean they are male and female or just that they have gotten use to each other?

The only answer that I could answer is the the two staying together

They may not necessarily be male and female.

With all species there is a dominant one and a follower.

As far as fish playing with toys, it would be funny but i don't know if anything I would say cause oscars are agressive and don't like other thing so it could seem like playing when they really are upset.