Your very kind feelings were clearly conveyed from the only 3 line question.
It is said that grandpa can go to the Pure Land of Paradise, but grandpa will decide where he should go according to his grandpa's work (actions) so far. So in the unlikely event that Grandpa is unable to go to the Pure Land of Paradise, unfortunately it is impossible for someone else to change his destination by manipulating something little by little.
Your kindness and compassion can pity, love, and nurture things, but as long as you are a weak person, it's almost impossible to help them until the end of their lives, even if they are immediate family members. Therefore, I would like you, none other than you, to become a Buddha and help Grandpa to your heart's content.
I have no intention of telling you to become a monk, but I just hope that none other than yourself will soon start practicing Buddhism in order to save your precious grandpa.
Namu Amitabha Buddha worship