Must I make up for my deceased grandfather who broke his fast in Ramadan due to illness, knowing that he fainted and broke his fast on that day?

The fast of one who fainted is valid if he awoke and continued fasting, and what he drank of water does not invalidate it because it was not by his choice. However, if he later broke his fast by his own choice, then if the fast was supererogatory, it is not to be fasted on his behalf. But if it was obligatory, then the details of the matter should be examined.