I'm very sorry for your losses.
If your coop is too hot to leave them in it at night you need to add ventilation, and all ventilation openings should be covered in 1/2" or smaller hardware cloth. Doors should be closed and locked with something a predator can't open. If they are not in a predator proof coop at night you are just going to be running a chik-fil-a for predators. Foxes can go up and over a fence like it's not there, they will sometimes kill every bird in there and only carry one or two off. Raccoons can open many kinds of latches if they are not the right type. Some predators will dig under walls and fences and get in that way. A game camera will help you identify what's coming in, but you will still need to prevent it from happening. Once they successfully hunt in your coop, they will keep coming back. If you post pictures of your set up it will help get you more suggestions on how you might get it better secured.