'Adopted Grandparents'

I wonderered if anyone had an oppinion on becoming 'adopted grandparents'
My one Grandson is grown up and it appears no longer really needs us ( he will be off to Uni this year) , and my daughter and son in law have become very distant since my he came out of the Army two years ago , he was in the Army for 23 years and it was ok for us to be around when it suited them but now they have made it very clear we are to be kept at arms length. We also like to know if there are any other Estranged grandparent out there who have been adopted and how they went about doing it. We have so much love and life experience to offer and would love some advice on this subject please .