You sound like a good person trying to protect your elderly family member your father ,and i respect that
.Regardless of how he might have looked after your interest ,you did an admiral thing protecting him in his old age.
Some very old folk are just best to be left in their delusion that this JW religion is the "truth" , it could do more damage than good trying to force them to face another alternative.
Just let them be.
Take care buddy.