Welcome and sorry for the bad news... Yes @MissSkittles is correct those are symptoms of respiratory infection. You will need a vet ASAP and there are also major changes required of your setup for this chameleon to survive.
If that's an outdoor cage you are correct it does not need lights. But, it needs to be bigger and more planted. Does he have access to shade while outdoors? How often do you mist? And what are the high daytime temps and night time lows in your area?
It's nice to have options based on observations. I tend to use LOD for every feeding with adults (Panthers) as they get less frequent meals and smaller amounts. For juveniles I used the Arcadia feeding schedule with Earthpro A as the main supplement then LOD at every 6-8th feeding. Just a...
I change out plants pretty frequently, but only to rotate them out with more lush ones. The chameleon definitely moves around the cage more whenever the change occurs.
I kept and "bred" dubia for the first year of having a chameleon but then around 14 months his appetite dropped enormously and I had a ton of extra bugs. Got rid of the colony and switched back to crickets because adult males I only feed 2-4 feeders every other day.
Looks awesome.... I think you have the diplandenia variety of mandevilla that is more of a trailing plant and may not grow up the cage as you desire. Diplandenia have small leaves and true mandevilla have large leaves. They both should work but will have different growth patterns.
Beautiful animals... Its cool that you got some younger WCs as opposed to full grown adults that could be towards the end of their lives. I would be careful with treating for parasites quickly, just make sure they are well established and stress free before treatments.
If it has been passed successfully there is nothing the vet can do besides charge you for a check up. I would just make sure to increase hydration to ensure it doesn't get stuck next time.
There is definitely a spectrum of plant preparation similar to branch prep. Some people go all out... Others just give them a once over. I just try to get plants from a reputable green house and simply spray them off with water thoroughly and re-pot into "indoor" potting mix to prevent gnats...
My guess is 6-8 months. You may want to fill out a husbandry sheet for review. Sleeping while being handled/during the day could indicate a health issue.
Excellent work getting him vet care! Now it's time to address your husbandry. In your pictures there are several things in regards to the cage that need to be corrected. You should still fill out the husbandry sheet for review.