welp, it depends if you want a nocturnal cat or a day catfish. usually, all the catfish that would fit a 55 gallon would be nocturnal. and beccause of your ocscars, the catfish wont be doing much in the day time. so it'll either seem lazy or you wont be able to see them at all.
for a 55 gal with 2 oscars, a pleco will do.
but if you want a change in catfish, a talking cat (ralphel catfish) is an odd-ball. you need lots of hinding places for this catfish and you'd never see it again, unless you sit at about 3 in the morning with a dim flashlight waiting for it to come out. i had one of these and they hated the light. they would only come out during the night, so dont expect excitment.
the catfish from the Pimelodid family (your pictus and 3 lined cat) are also nocturnal. your oscars will also make this fish extremely boring by forcing it down to the ground. i had 2 of these too with one oscar in a 55 gallon. when the oscar reached 7" it made the catfish scared, regardless of the time of day. one time i had to move the ocsar out for a while and the pictus seemed so happy. they swam so gracefully around the middle. but when the O came back ,back to the ground. so the only catfish i would recommed would be a pleco. i cant think of a loach to put in your tank..so a pleco is probably the best bet to go with.