JM75, I'm so sorry you're going through this. My dad and I also have the same conversation about my sister.
I would strongly suggest starting your own thread about your own situation if you want to receive more responses, since this is an old conversation. You'll find people in SR are more than willing to help.
It took a long time for my dad to see that there was a problem. Heck, it took a long time for ME to see the problem. Unfortunately, the eye opener for us both was when my mom, then he, got cancer. They needed both our help, but my sister bailed out.
One question that I often ask myself as a parent... "Am I doing this to make myself feel better, or is this truly better for my child? I posed that question to my dad during one of our arguments, and he couldn't really answer.