50% changes every other day is a bit extreme if you have the right size tank and good filtration. The bigger the better.
You really need to upgrade immediately. I'm assuming your current tank probably isn't cycled. This means that you really need to upgrade, and get some Seachem "cycle" to help get you going a little faster.
I have 3 oscars. I just picked up a new one tonight. From walmart... only because they got a REALLY good shipment in.
IMG_5566 by
muffywrx, on Flickr
Oscars are fun, and if you really want to keep them alive and watch them grow (they grow FAST), then you need at least 55gal per oscar MIN, and recommended 75gal per oscar. I have a 125 gal for 2 oscars that hopefully will pair up and a 75 for the other. You can find good deals on craigslist or here on MFK a lot of the times. You can keep them in a 55 or something for now if you find a decent deal, but please get them moved soon or else they will die.
The reason they are going to die is because in the 10 gallon, while they have plenty of room it seems, their waste (=ammonia) will build up, which is really toxic to fish. And because you probably just set up your tank, you have no beneficial bacteria (BB) to convert it to nitrite and then to nitrate. Nitrite is also toxic, and nitrate is only slightly toxic. In a 10 gallon tank, ammonia is going to build up really fast. And your fish will die. If it were cycled, nitrates would build up really fast, and while less toxic, you would have to do water changes every day and this is hard on the fish too, just not as bad as poisoning them.
At least get a bottle of seachem "prime" as well and it will detoxify the ammonia for I think up to 48 hours. The BB can still feed off of it and can still develop ...
If you can't do any of this stuff, you should take the fish to a local fish store (not back to walmart, they will probably flush them, and not to petsmart or petco). Look up one online.
I hope some of this was of some help, and I hope you take it to heart.
Keeping 2 baby oscars in a 10 gallon may look okay, but believe me they will produce way too much waste (and you won't know it until they are dead) to live in it for very long, at least not without suffering
I hope you decide to keep them and upgrade to a very large tank to accomodate 
