These are the wild babies that were found on the road, correct? Like they fell out of their nest?
I agree, there is no way to know why he is crying constantly, but the fact that he is doing it is not normal, and something is wrong. I saw the photos of them in your first post, and they were only a few weeks old then, at most, so I'm assuming you're still hand-feeding them the Kaytee Formula?
When did he start the constant crying, how long has it been going on? Is his crop emptying properly after you feed him? Do you smell anything weird or sour coming from his mouth? It could have to do with the hand-feeding, like a yeast infection or other issue, or it could be another illness, or an injury from when they fell, etc. There's really no way to know unless it's something obvious like his crop not emptying, a sour smell from his mouth/crop, etc.
You need a vet...You said that there are livestock vets around you, so you need to find one that specializes in poultry. It's not as ideal as an Avian Vet that deals with parrots, but birds are birds and it's much better than a general livestock vet. Something is very wrong if he just started crying constantly and hasn't stopped, and the fact that holding him brings him some comfort yet he still doesn't stop making noise tells me that he's most likely sick or in pain.
Also, what country and city/town do you live in? A lot of the time we can find an Avian vet near people in foreign countries that they didn't even know existed...