Oh, how sad to have to give them up!! I work in a pet store and Im one of those rare employees who tells the TRUTH!! No you cant keep 5 baby oscars in a 10 gallon. Thats so true that people believe they only grow to the size tank they are in. Just like goldfish, they will keep growing and getting more and more deformed. Our store accepts trade ins constantly and I think the thing we see the most are oscars. This one time we had the most awful looking oscar. He had a huge hump on his back and his shape from the side was almost round like a discus. It was the saddest thing ever! I so wanted to take him in because I felt sorry for him but I couldnt.
Great point too that you brought up about the feeders. So many people get these fish for the thrill of watching them eat smaller fish but dont realize just how unhealthy it is for them. Do goldfish live in South America? No! So why feed them to them? Your oscars sound like they were so well cared for and I'd love to see pictures if you have any.
I was reading an article awhile back in Koi World magazine about other fish you can keep in your pond, and the author had a heated pond with oscars in it! He said they lived right alongside the koi and goldfish and got along great with them. Not only that, with all the extra space they got huge and had such nice bright colors that you dont normally see in a tank. Also the oscars would sit there begging just like dogs for their food, along with the koi.