Well, I really don't want to get in to keeping a 13" oscar in 33 gallon tank. It just doesn't seem to me like that is fair for the oscar. I know that pellets are not as messy as flakes, perhaps I should clarify, that I really do feed my dovii, "sticks", by Tetra, which are really just pellets that are in a long and narrow form rather than round, but maybe that has something to do with they way they are eaten.
Although keeping one oscar in 55 gal tank is not really good, keeping 2 in a 55 is asking for trouble in my opinion since as they get bigger and older one is going to become dominate and probably reek havoc on the other. Then again maybe nothing will happen.... I can only share with you what has been my experiences in the past, and what I have heard from other fishkeepers. And that consensus is; it is not a good thing.