Glad to hear they're still hanging in there for you.
Sorry for not responding sooner but I've been dealing with my own Jackson's xanth babies and haven't been on the forum.
What a shock to have to deal with babies within days of getting a new cham.
I don't know your level of experience with Jackson's but their care differs somewhat from Veileds and Panthers.
The Jackson's really like higher humidity and lower temperatures than most species, so if the babies are kept around 70% RH and around 70-75 degrees, it will help them to remain hydrated.
If they are always a bit dehydrated, that can cause an appetite loss.
It would be very difficult to extend a tongue from a dry mouth.
It may be like when you're rather thirsty and your lips stick to your teeth
They should be kept away from a/c vents, since a/c dries the air..
There is the possibility that there is something developmentally wrong which is keeping them from eating--- though I'm surprised they're still alive, if that's the case.
I hope you've been spraying the enclosure and leaves a few times daily.
The fruit flies are the flightless types, I hope.
Babies need to eat throughout the day, so the more food, the more often, the better.
Here is a link to some good info about Jackson's with details on temps, humidity, etc.
https://www.chameleonforums.com/care/caresheets/jacksons/
Perhaps they have been eating--just not while you've been watching....
If you've lined their enclosure with paper towels, the tiny little poops will be easier to see.
They may need a huge number of flies wandering about in order to be able to catch some.
You can put a piece of fruit in the cage, which will attract the fruitflies, so they will stay in the cage longer.
Maybe the babies will eat some extra small Phoenix worms or baby silkworms.
The temps in the late day sun may still be too high for the neonates, as they may not "know" to regulate their body temps very well. 75 to 80 is a good basking temp range for babies.
Hopefully, an increase in humidity and more frequent, generous meals are what's needed, as those things are easily rectified.