I like to start off by express my sorrows for your loss. It is never easy to lose a pet no matter what. Now I'm no expert on chickens, but my guess would be they either do not have enough shade, aka a place to go when the sun gets too hot or they were not hydrated enough. I'd suggest either looking into an automated water feeder for them or building some form of structure to allow them to take cover on days of intense heat...or both things for that matter.
On a side note, if you are In college and going to be going away, if your parents are not going to take care of them for you, you might want to hold off for a bit until you can spend more time with them. It wouldn't be fair to anyone if enough time and effort was no able to be spent.
Good luck...and remember, think of what's going to be best for the chickens.