I think if I remember right about the cornish chicks is to pull the feed from them for 12 hours in the day. Meaning free feed them for 12 hours and pull feed for 12 hours. They will eat constantly as they don't know when to stop. There is someone on here that was able to keep her cornish past the life expectancy, I do believe the trick was pulling the food. So you could give them food from 6am-6pm then pull the food til the next morning at 6am.
If they are panting I would say they are feeling uncomfortable, probably due to their weight. Make sure they have plenty of water. In the picture I see you have the little chick waterers, you may want to get the bigger ones, like the gallon. I would be concerned their beaks are too big to get enough water from the little one.
Definitely look into getting some sort of vitamins for them so their legs can stay strong.
I hope they live long for you as pets. Just be prepared just in case their bodies cannot hold up for as long as you would like.