To: IAAL

Good evening. My husband is very concerned about the finances of his aunt and grandmother, who raised him, and that's why I'm writing.
This all takes place in Georgia.
My husband's aunt has a 22 year old son who was diagnosed in childhood with learning disabilities and is currently on Ritalin or some sort of behavior drug like that.
Anyway, this son has run up over $3,000 in phone sex charges. His mother is paying her mother (my husband's grandmother) for these charges b/c the phone bill is in the grandmother's name. All 3 of them live in the same house, which is rented from an absentee landlord. There was never a written contract, just an oral one between the landlord and the late grandfather. The son frequently loses trucking jobs and contacts his mother for Greyhound tickets and other expenses, which she pays for. My husband is worried because this family is slowly going into hock because of this son, and my husband hates to see it happen.
My questions:
1) Is the mother legally responsible for paying the son's phone bills and other debts?
2) What other recourse legally does she have? There's even been some talk about not letting him come back home the next time a job ends, or even committing him to the state since she is having trouble keeping up his welfare.
My husband does not have the resources to take this guy in. And especially if the son goes off his behavior medicine, he's not safe to be around our toddler.
Thanks in advance for your help.