Whats wrong with my Gandmother?

I think she needs to be evaluated. If she has a condition such as dementia, she will need appropriate treatment and support. Also, a mental illness should be ruled out. Perhaps someone in the family can talk calmly and practically with your grad dad to get him on board. A starting point may be the primary care physician. You also want to make sure there isn't some medical condition causing this sudden change in her personality.