Mealworms aren't very nutritional, especially as a staple diet. Their shells are also hard to digest, especially if your temps are only 26-30, these need to be up around 38-44C under the basking spot. This will probably explain the lethargy, I'd imagine (?) the sore tongue is due to the mealworms. If u insist on feeding these to a juvenile beardy, they should have their heads cut off so they can't nip them, even fed tail first. Crickets or woodies are a much better food source.
When u say natural sunlight, are they in a glass enclosure & next to the window? If so, UVB doesn't penetrate thru glass or thick plastic, so in effect they don't get any needed UV this way, as well as risking cooking/burning them. You really do need to invest in a UVA/B light as well, & move away from the sun. If on the other hand you put them outside in a non-glass enclosure for the sun at least 3-4 times a wk, this is fine.
Re dusting the fruit, if it's eating all the fruit that's fine, but it's usually a safer bet to dust the live feeders in reptical as they're more likely to eat all these, thus getting a better effect. Bananas should only be fed as a treat, once a wk, max twice. Get onto some bokchoy or wombok cabbage, leave it a bit chunky, they do need their greens.
Let us know about the natural sun thing, & PLEASE put a stronger heat light (100-150W) in or you'll end up losing your little fellow. Cheers
