I will be out of the country for 2 years and my son whats to finish high school in the US. His Mom wants him to go too, but he doesn't want to go. His Mom also has a husband that does drugs and can not afford to provide care.
I don't know if she will agree to our son staying at grandma's as they never had a good relationship. Grandma is the most logical care provider as she lives close to the close to the school, has the money and means to provide for our son. The mother will end up seeing her son more regularly this way and he will not be left stranded for 3 hours for Mom to finish work to pick him up from school.
If the mother agrees to this arrangement, do I need to have a letter of agreement notarized or should I file for change in physical custody or guardianship for Grandma?
If there is an active Family Law Case, a Guardianship cannot be established. The Family Court can give Grandmother legal Custody. If you and mother agree this would be best then you can submit a written agreement to the court, make sure Grandmother consents in writing and the court can grant Grandmother custody.
It is important to seek competent legal advice when involved in any litigation, including child custody. The above in intended solely for educational purposes and is not legal advice. No attorney-client relationship exists by means of this answer.