I am wanting to see what else might be recommended for this enclosure, I am currently housing two panther chameleons in this enclosure and have noticed they are starting to darken a little so I would like to help them stress less if possible.
Firstly, chameleons should not be housed together. They will fight, one will become more dominant, and the other so stressed out it gets sick and eventually dies.
The enclosure needs a lot of work. As it stands, it is nearly empty. Remember: Empty space is wasted space! And by that metric, your enclosure is about 80% wasted space.
The biggest problem is how empty and open it is. You should aim to recreate the look of a lush rainforest. Your enclosure needs a ton more foliage - preferably live plants - for your chameleon to climb and hide in when they want to get away. Chameleons are also 3-dimensional movers. They need ample opportunities to move up, down, and side-to-side. It is super important to provide as many horizontal perches/branches/vines as you can, like a ladder throughout the cage. The vines in there are not going to cut it, unfortunately.
More specifically, you need to move all the vines up significantly. As they are placed now, your chameleons cannot get close enough to the basking light and UVB to benefit from them in any meaningful way. Also, the carpet in there needs to come out, as it will do nothing but harbor dangerous bacteria which will get your cham sick