I actually deleted a part of my post suggesting a vulture catfish, ultimately thought a 130g would be too small for an adult vulture. In my opinion it's a little tight for any suitably sized bottom dwellers+2 adult oscars. There are some midsized pims like ornatus or goldiella which could still potentially be eaten. Some of the larger growing synodontis cats could be good like angelicus, batensoda, or the commonly available eupterus as long as it is of substantial size when introducing and you provide a log or something for it to hunker under. I've actually seen this combo in action at a LFS demo tank for years now--large adult Oscar with a supersize batensoda 10"+ in a ~125g tank
Big issue will be temperament of the oscars. If one or both are particularly nasty or if they pair and start to breed there will be nowhere safe in that small tank for any bottom feeder. They might not kill it but it will not have a fun life being harassed, fins, whiskers, and eyeballs nipped, and chased around constantly when the Os are bored. Could work with sufficient space and hiding spots though.
This. My Oscar Brick destroyed a full sized synodontis catfish. Peeled off the skin, broken back, missing eye and fins. On the maintenance part, oscars are unbelievably messy, especially during growth spurts. As a teenager Brick put out his weight in turds daily, leading to brown algae blooms on a weekly basis. Just piles of the stuff.