Your gall bladder isn't really deadly neither are kidney stones.
At least not to the point where you need emergency care ASAP or you'll die.
Both of those are just more painful than anything.
Though Appendicitis is something trry about since he said it's more in the lower area of his right side. Kidney stones you feel more in your back and a bit in your abdomen if they've passed into the bladder. As far as gall bladder, I'm guessing you mean stones? That's on the right side as well but it's closer to your rib cage, it's almost just right under neither it on most people.
They can be deadly. I didn't say that their equally as dangerous. The longer you ignore it the worse it can get.
If he's feeling that bad he needs to go to the hospital.