Afraid not generally, they require land to come out onto and bask under heat/UV bulbs a lot of the time, so for it to have space for an oscar/knifefish the tank would have to be pretty huge (and considering terrapins are messier than oscars, and oscars themselves need big filters...the filtration would have to be massive too).
If you could get the tank right...then it might be OK, but I wouldn't recommend it. Chances are the terrapin will end up taking chunks out of the oscar (which may not like the terrapin).
Knifefish is more likely to be safe because it should ignore the terrapin, but in small enclosed spaces it will probably eventually be bitten.
Terrapins can often live fine with goldfish and koi in ponds though, so it's not guaranteed to fail if the tanks big enough, but it's a risk.