You can try feeding them anything except obvious things like hot peppers, etc. Some things, like Brussels sprouts, broccoli, cabbage etc. will make the water smell, so don't feed that.
Try to feed as much veggie material as you can, it will keep the water cleaner. Flake, pellets, etc. are very rich and I wouldn't feed them every day. When you feed flake or pellets, make it veggie and algae based - Spirulina, algae wafers, veggie flake, etc.
Try to feed so that nothing is left behind, that may mean very small meals more often rather than one or two big feedings.
Goldfish are great fish but they can be a lot of trouble, trust me
You will know when things aren't right, they will start getting frayed fins and be lethargic, they may have a reddish appearance to their fins or gills.
Incidentally, whatever your room temperature is should be fine. My goldfish (black moor) are in an unheated tank and were very frisky and happy in winter, when their tank was 68.
Try to feed as much veggie material as you can, it will keep the water cleaner. Flake, pellets, etc. are very rich and I wouldn't feed them every day. When you feed flake or pellets, make it veggie and algae based - Spirulina, algae wafers, veggie flake, etc.
Try to feed so that nothing is left behind, that may mean very small meals more often rather than one or two big feedings.
Goldfish are great fish but they can be a lot of trouble, trust me

Incidentally, whatever your room temperature is should be fine. My goldfish (black moor) are in an unheated tank and were very frisky and happy in winter, when their tank was 68.