Like most JW's it is likely that your father has steeped himself in the religion more so these days, not out of a growing concern for others, rather it is because he realizes he has reached the stage in life where he is "circling the drain" and time is running out.
Many JW's have convinced themselves that they love their neighbor but the main motivation for them is to save their own skin. If he was motivated by love, he would do all he could to reach his own grandchildren instead of focusing on knocking on the empty door of strangers. If he focused on his grandchildren however, he'd have to be more than a friendly stranger at the door who can walk away as soon as things get tough. With his grandchildren, he'd have to be himself and he'd have to stick around even when they asked tough questions that he has no answer for. It's easier for him to go through the motions and choose the other busy work that is part of being a JW. That way he can feel good about not having really done anything real.
Coming to terms with ones own mortality is something that is best done gradually over ones lifetime rather than all at once. You are kind to let him continue on with the magical thinking that gets him through his days and nights, now that he has reached this stage in life. One day when he is gone, you will look back and feel good about having done your part to make his last years reasonably peaceful.