Can't he just use his Brazilian PP to go back to Brazil?
I would suggest getting the notarized document written in both Portugese and English. You may want to include language giving the adults "medical power of attorney" so the can make emergency medical decisions until able to contact you via phone. It may be worth having a lawyer draw up the document so all nuances are covered and it is clear what you intend. Perhaps you could contact the US Consulate in São Paulo to get better information, since you live there.