So very sorry to hear that.

I know that you did a lot of research before they arrived.
It always is so sad to lose a pet, even if they have been with you for a short time.
Sadly, when chams show symptoms of illness, there is not a lot of time to spare.
It could be that your cham already had something going on healthwise before you got him but the only way to know what happened to him is a necropsy by a reptile knowledgeable vet.
A new environment is stressful and if the cham already has a problem, like parasites or an undetected infection, it can overwhelm them much more easily.
Some wild caught chams seem to be unable to adapt to captivity and perish without a recognizable cause.
When an illness or death occurs, it's always a good idea to take a careful look at the setup and care to be sure everything is spot on, to protect the health of your other cham.
Sometimes things as innocent-seeming as stagnant water that has been accumulating beneath something can lead to respiratory infection.
A fecal exam for the female would be very wise.
If you don't already know of a qualified vet with lots of reptile knowledge, you can have a look at this ARAV page
http://www.arav.org/find-a-vet/
this post
https://www.chameleonforums.com/veterinarian-resources-67/
search the past forum posts or ask for help.