They are not coral they are deer antlers but I get your point (pun intended). These girls are pretty docile. I have a back up tank if things don't work.Most common plecos grow to 18+ inches and need a bigger tank. Anything smaller will probably get eaten.
Oscars are territorial ambush predators that don't like tank mates with the exception of a partner that they choose. If the Oscars were 2-3 inches you could add other fish and hope they get along when the Oscars mature, but adding anything to a tank with two x 7 inch Oscars is asking for trouble.
You need to change the angle the bits of coral are set up at. The fish could panic and swim into them and get damaged. the pointy bits should be facing downwards. If you want something to increase the pH then use limestone rocks instead of coral.
The blond variety looks very intersting. Haven't seen such one in our country before.
I saw another aquarist with deer antlers in his tank that's where I got the idea I thought it look pretty neat.I think the antlers are interesting... aside from the poking during occasional scuffles ( they could be turned down ) but I expect they will slowly dissolve in the tank, making the water harder, than what you may be wanting, with Oscars in the tank... not sure what your water conditions are, but I'd expect it would be similar to running coral in a tank, & raise the calcium level???