oscars?

i recently purchased a pair of baby oscars not sure if there female or male,
i was wondering does anyone know how to tell if there female or male and
also i was reading that when they get big they turn aggresive, the two i
have in my tank are really getting along and following each other everywhere
in the tank, will; they turn against each other when they grow up..? i have
a fairly large tank 8 metres long so they will have heaps of room to move
when they get bigger, cause ive heard cichlids are very territorial..