Thanks everyone.
My Oscars might be paired up? I'm not sure. They are best pals, do a lot of synchronized swimming and are complete goofballs. It was funny, actually. The white one was in the tank first.
When I introduced the larger black one, it was scared. The white one came over and shielded it from the whole tank, and swam on him like a piece of armor. It was astonishing to watch, really. They have been pals ever since.
Right now the Red Devil seems to think its an Oscar, as he follows them around and swims with them. My female Jack Dempsey is fairly aggressive, and puts everyone in their place minus the Oscars. The Red Devil wants no part of the female JD, but will calmly stand its ground to everyone else. It isn't aggressive in the slightest, but I know what to look for.
Lots of good ideas in here, and I'll be sure to listen to all of them.