Just a suggestion...
Given Grandpa's circumstances, give yourself permission to go with your gut and follow your heart. Trying to even loosely follow a certain dosing method/protocol may not apply or be best for him right now. I've known caregivers in similar circumstances who will routinely skip shots on those low preshot numbers. Another option is to shoot as needed... when you feel the preshot numbers is high enough. You don't have to follow a strict 12/12 shot schedule. One day you might want to shoot at +12... another at +15. The goal is keeping Grandpa as comfortable as possible and you rested enough to care for him. You make the rules.
I hope you both can get a few naps in today...