I had two Oscars in a 75 gallon for awhile with no trouble. You just have to watch the nitrates and have alot of filtration. Then of course you have have the aggreession work out. In a 90, you could do the two Oscars and a firemouth or two if they got along.
Angels are pretty versatile, in a communityish setup with smaller fish they will be peaceful because the small fish are not seen as a threat, but they are surely not wimps and stand up to other fish that mess with them