Simply put... I don't get it...
The Oscars will be fine in the critter keeper for about a minute... provided you didn't try to keep them in there long it's fine... but a total waste of time as they will outgrow it exceptionally fast... By the looks of it when the picture was taken they had already reached that point
As for your filtration, you didn't give us enough information to make any logical comments. What you explained might work fine, and might not work at all. Details my friend... details....