Old timer crawling out of the woodwork to help a friend

[msme]

Hi everyone! Long time no see. Lots of news but I will save that for later. I need some info on OK law about custody & visitation.
I have a friend who is the guardian of his adult child & his grandchild from childs first marriage. The second marriage produced another child. There was a divorce in TX about 10 years ago. The adult child suffers from significant mental health problems & has spent a good deal of time institutionalized & is currently. He has raised the first grandchild. The second ex disappeared with the child, shortly after the divorce was final. The divorce decree gives his child standard visitation but they have not seen or heard from them for nearly 10 years.
Recently he located them. He has not made contact for fear that he will run again. I told him that I think he will have to get jurisdiction transfered to OK before he can get anyone to pursue reunification counciling. Does anyone know if this is correct? Or what he needs to. We will welcome any & all suggestions. The grandchild really longs for the sibling.
Thanks & Hugs to all
Betty