I think there might be some family tension/dysfunction going on.
SG is the golden girl---wildly successful, famous, talented, very wealthy, AND she does not have to do the heavy lifting with their Mom's daily life. She has huge worldly concerns and she has fame and fortune. There's nothing wrong with that.
But AG is living a very different life from SG's.
AG and TC were reportedly the caregivers for Nancy. It is a lot of work. I know everyone is saying NG is as sharp as a tack and very independent, etc. But there are still a lot of things that she would need help with in many ways. It is kind of a thankless job.
I've seen this kind of family dynamic before---the Golden Child is celebrated and put on a pedestal in Mama's eyes, and when they return to the hometown, there is great fanfare and excitement etc.
The child that stays home to do the boring caregiver type things gets very little attention or reward. In fact they get some negative attention because they need to remind elderly parents to take their meds, go to the doctor appts, and convince them they are getting too old to drive safely or to take care of their own finances etc.
It can become tense and divisive. I've seen how it works sometimes.
It would not surprise me if there were some rifts in the family and perhaps involving finances.