I wouldn't do it, either. It's not a matter of wasting money, either, IMO, but one of being capricious with living things. 60 l is generally small for two goldfish alone. Keep in mind how big they can get - they're almost guaranteed to break six inches, could get to 12, and as stated above, 18 inches isn't impossible for some varieties. They won't stop growing to fit their tank - they'll become stunted and likely die shortly after. They can live twenty or thirty years with proper care.
They're insatiable eaters, and they've got a huge mouth. I've watched a goldfish barely three inches long eat a male guppy. The neon tetras would be doomed.
If you want to make sure you're fully prepared for it, set up a 20, preferably 30 gallon tank with a powerful filter and keep the goldies in that by themselves. If they get huge, even that could prove too small, but you and all your fish, gold and tropical, are in a far better places for it.