Unfortunately, there's a lot of information online that just isn't true, and any rules that use inches per gallon as a way of determining how many fish can fit into a tank are wrong. Separate species of fish are too different to lump into one rule.
The main problem with your tank at the moment is that the oscars will outgrow everything else pretty quickly and most likely end up eating them. The Chinese Hi-Fin will also outgrow the tank eventually, as will the black ghost knifefish. It's also usually recommended that you only keep one black ghost knifefish per tank. Depending on the species of bichir, it may also outgrow the tank. If you know what species it is, that would help to determine if it can fit or not. Also, if your pleco is a common pleco, it will definitely outgrow the tank. One other thing to keep in mind is that glass catfish are best kept in schools.
You do have a few options regarding stocking. You could get rid of everything except for the ropefish, upside down catfish, and the bichir, since those are the only fish that could really stay in there long-term. You may also be able to keep the glass cat, but odds are the bichir will end up eating it. Then, you could possibly add some other fish that can live with ropefish, bichir, and catfish.
Your other option is to upgrade to a much bigger tank and keep the oscars, one of the black ghost knifefish, and maybe the pleco or the bichir. The ropefish would probably end up getting eaten by the oscars, and so would the upside down catfish, unless you grew them out before adding them with the oscars in a larger tank. The glass cat would definitely be eaten by the oscars. I would get rid of the crayfish and snails either way, crayfish and fish don't usually live together well. I would also get rid of the Hi-fin, they just grow too large for most home aquaria. If you wanted to keep all of the larger fish, I'd recommend at least a 120g at first, but bigger would be much better.
Hopefully, this helps a little bit. Good luck with whatever you choose to do!
