I agree, they should be breeding size already. My 8inch uaru started laying eggs at 7 inches. Uaru eat there eggs for the first few times. It may just take 6 or more attempts befor they get it right. I would keep them conditioned for the next few months and keep your fingers crossed.
I get my female to lay eggs by feeding very lightly for two weeks with regular water changes, keeping the water temp at a steady 26C. then i feed heavely for one week on alot of frozen foods. I then do a large water change of 50% and raise the temp to 29C. within 24hrs of that water change, i usually have eggs. But the pair eat them within a day or so. They have done this 5-6 times now. I have not given up, but i have stopped trying to trigger them, and will let them do it when their ready. I now just keep the temp at 29C and feed regular, with a water change of 30% every 3 days.