Is the cage humidity only 50% at night even with the mistking? Or is that the humidity before misting? If 50% is your daytime humidity then that should be fine. Just remember daytime humidity should be between 30%-50% and night time is 75%-100%. If your daytime is 50%, then that is fine. But if your nighttime humidity falls under 75%, even with the mistings, then you should hook up the humidifier to the fourth cage as well.
If you look at the care sheets from
https://chameleonacademy.com/caresheets/, you can see that Veiled chameleons and Jackson's chameleons essentially have the same temp and humidity requirements (only that the ambient temp veileds can tolerate is higher). Make sure that you are hitting these temps and humidities for all your chams. Veiled's are more montane than once thought.
The lower you can get your temps at night, and the higher you can get your humidity at night, the better off your chameleons are.
A good point to mention
@CasqueAbove, as said above, Jackson's chameleons are more sensitive to supplementation than veileds due to different metabolic rates. I use arcadia earth pro A every feeding and Repashy Calcium Plus LoD twice a month--even though I have a solar meter to ensure proper exposure.