From what I remember from when I had a couple oscars and started researching more into them is that, generally, 75 gallon for one oscar is a good rule of thumb, 125 gallons for two... I can't quite recall how much of that was due to their biological load and how much of it was due to their territorial sense of space, but looking at the long list of other fish in the 100 gallon tank, I'd have to think that you might be pushing the limits of overstocked, which is why you're having problems with filtration...
Maybe you could find ways to keep filtering, but what I'm surprised about is that your oscars haven't killed any of the other fish yet, especially after seeing mine do in some pacus that were bigger than them...
I'm not so informed though about the world of aquariums so take what I say with a grain of salt. Also, I love your oscars. The ones I had looked exactly the same as yours almost, one tiger and one albino, almost the same size even.