I kept bichirs with my oscar in the past with no issues. As others have stated, it won't be an issue unless the oscars can slurp them up like spaghetti.
With all the fish at 2" you are probably ok for the time being depending on how fat the bichirs are. The oscars will grow faster than them, so perhaps you'll have to move the oscars to the bigger tank and let the bichirs catch up in a different tank. Having bought lots of polys over the years, I have had to spread them out among my tanks depending on size to prevent cannibalism. There is always a change that you'll get a runt or something and it will never catch up to the oscars, though.