Must my brothers and sisters make up prayers during which they touched or prayed on impure things due to my scrupulosity, or is repentance sufficient?

The cure for whisperings (waswas) is to disregard them and pay them no attention. Even if we assume that what you mentioned is true and not merely a whispering, you are not obligated to make up prayers for any of your siblings. Repentance alone is sufficient for you. It appears that what you mentioned is merely whisperings that have no reality. Therefore, you must ignore whisperings in all their forms and manifestations, disregard them, and pay no attention to any of them.