OK,cool. You're going the adoption route then. I was stopped in my tracks when we found out it may take three years to process... yikes. My wife talked to her lawyer today and discussed the pure guardianship route. He said it will require a court order and a few thousand baht but easy enough to do. The childs dad is in jail and cannot take care, his family cannot take, and the childs mother is married with another kid and cannot take care... all are willing and able to to sign whatever needs to be signed to relinquish claims on the child. My wife told me the name of the process in Thai which translates roughly to guardianship but cannot write Thai language here to tell you...but in the end she'll (the childs grandmother) be the legal guardian and... as far as the rest of it goes we'll need to get the lucky 5 year old a Thai passport, translate the custody documents, and apply for visa which should be a rubber stamp affair as far as I can see.
And of course this which we have already covered:
One of the child’s parent(s) or legal guardian(s) must have a valid B1/B2 (Business/Tourism) visa at the time of the child’s application