Oscar Trouble Or Not??

Could be pairing behavior, but they usually will stop at lip locking and won't cause injuries to each other as bad as your describing. At 5inches they may still be a bit too young to start spawning, generally 6-7inches is when they will begin showing that behavior, provided they haven't been stunted and their age is reflected in their growth. If your goal is to have a a pair, and it would almost eliminate the aggression between whichever two fish pair off, I'd suggest getting another 2 fish similarly sized, quarantine them in a separate tank for 4-6 weeks to make sure they aren't harboring any diseases, and then add them in with the other two. Once you get a pair, take the two that haven't paired and return them to the LFS.

While there isn't any way to tell, you might just have a gender combination that isn't working. Most of the time Oscars arn't particularly agressive so it must be something about those two individuals.

Seems like normal behavior, I have 2 oscars and the larger attacks everything in the tank. My oscar is about 7inches and he chases my 12inch pacu away. I dont know, maybe its a territorial thing.

Do you know the sex of both of them, maybe they are the same sex? ( both males or both females)

Do you know the sex of both of them, maybe they are the same sex? ( both males or both females)

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Therein lies the issue (potentially) Oscars cannot be sexed acurately without disection, and that usually renders them incapable of breeding.
NatakuTseng's advice is probably the best approach if you want a matched pair. if you don't. just find a new home for one of them, as they may very well kill each other if left together.
Dave