Lobelia is very strong; that is why it is not recommended for children. It is antispasmotic and an overdose could lower a child's respiration. But since you have some experience with it, why don't you dilute it so that he gets only a partial drop per dose, and monitor him really closely, then adjust the dose as necessary.
Why don't you try to find a group home school for him? Or make a plan for him to deal with his current situation? Any alternative would be better than weeks and weeks of chest problems. You sound like a really caring mother; I am sure you will do what is right for him.