They Never treatd me well but a thought has occurred to me, they have one grandson who lives nearby and is friends with their biological son. His mother was their first child and has passed away. He comes over sometimes to do jobs that I cannot. As they possibly have dementia as well as narcissism, does anyone think there is some undue influence going on. He is a substance abuser as is the brother. I feel as if I have been making excuses for their conduct all my life but maybe this is possible. Any advice would be appreciated. Thank you.
It is unfortunate that the family isn't supporting you any longer, but there's another way to view the situation: if this is how they might treat an adult, be glad that you no longer are under their jurisdiction.
Treat it as a learned lesson: you've learned how not to treat any of your children. That in an of itself is worth a PhD in child rearing.
You've probably gotten as much good from their care as you can; leverage it and move on, living your own life w/o being obligated or involved with them.
I don't mean to sound cruel; it's hard to imagine the heartbreak this could cause you, but that could only increase if you're not able to move away from them and create a life of your own.
Sounds like you're still caring for them in some capacity(I'm not sure why), but it might be time to cut your losses, and get on with your life away from your parents. I just don't believe an inheritance is worth all the aggravation. You'll be just fine without it, and might actually find your joy again. That's what I'm hoping for you.