Is it permissible to participate in the transplantation of organs removed from brain-dead individuals or from those whose heart and breathing have stopped and lost consciousness, given the doubt concerning their death, and the fear of dismissal or punishment in the event of refusal?

If the specialized doctors in your country unanimously agree that brain death is considered a legal death after all brain functions have completely and irreversibly ceased, then there is no objection for you to participate in organ transplantation from brain-dead individuals. This is what the Islamic Fiqh Academy has decided. As for someone whose heart and breathing have completely stopped, they are truly dead. You must disregard obsessive thoughts and seek refuge in Allah from them.