I'd like to speak to the question of why your grandchildren don't want to know you. I never knew my own grandparents. As an adult, I wasn't very interested as they were strangers. In fact, I've been angry when my parents have tried to foist my 'family' on me because I don't see them as my family. There's been so much of my life they haven't shared so it would never be the same. They can never be more than acquaintances. I'm sure there are different stories out there, but that is mine.
As far as the blog, stories like, my grandmother grew up on x street, worked at x place, spent her weekends doing x hobby. That's one thing. If you start sharing about the generations after you (i.e., your gc's parents) I think you are on shaky ground. My parents' stories overlap with mine and I wouldn't want that shared so publicly unless I choose to share it. If my grandmother started writing about that, it would seal the deal as far as not wanting contact with her.
It sounds like you are wanting to use the blog to bring your grandchildren to you. It's unlikely that will happen that way. It would be a good idea to talk about it in counselling and maybe find a better way to reach out to your grandchildren, if that is what you want to do.