[Saya]

My first thought upon reading this was - what a wonderful thing! How wonderful that your son's birth grandfather wants to ensure that he is included, and that your son will know that his first family still thinks of him as one of their own. I understand though that you might not feel comfortable giving them lots of ID'ing info. Given what Belle said above, would you even have to give them info OR hire a lawyer? Would it be enough for the birth grandfather to just write in the will that any children placed or parented of his kids would be in the line of inheritance?

Editing because I just read your new post - if you have an interest in your son meeting his birth grandfather, why not make it happen? Why not use this as an opportunity to meet him and see if the 2 of them can have a relationship going forward? Just because the adoption began as semi-open doesn't mean you can't open it more now. It sounds like more openess might be a wonderful thing for everyone going forward.