Oh and your second problem is the the brother and sister live in Alabama not Georgia where the grandaughter resides apparently with the grandmother.
(4) In the case of a resident who has not been adjudged incompetent
by the State court, any legal-surrogate designated in accordance with
State law may exercise the resident's rights to the extent provided by
State law.
Code of Federal Regulations]
[Title 42, Volume 3,Page 502-571]
Notice it says any legal surrogate and the words state law.
The other relatives live in a different state, therefore they are not subject directly to the state law. The granddaughter was the closest living legal next of kin.
I understood that she just looked after her - but not lived with her...and has POA over finances - about $500,000 in the kitty? Maybe someone didn't want to see that get drained off on hospital bills...