I can very much relate to how your grandfather felt when the religion expected him to reject his blood relatives in favor of strangers.
This did not sit well with me either and I had a rude awakening many years ago on a Thanksgiving holiday when I was all alone like some idiot fighting a private war - meanwhile I could have been enjoying a delicious meal with people who were not judging me!
What a fool I was!
I opted to "fade" and this was one of several reasons I wanted out. Shortly after my "fade" I re-established contact with relatives and old friends before it was too late and this was priceless..
The zealots in the religion who wanted to isolate me from the only people who ever cared about me can go to hell - along with all the ones who criticized and ostracized me for having a full time job. I couldn't help feeling some people were mean or just plain envious....I'm glad I followed my gut and never listened to these people.