Thanks! two more questions regarding cosponsor (I-864) and US do

1. My aunt has retired for many years now live in China most of the time.
By reading online, I believe I have to file I-864 for my Dad's case as well as cosponsor right?

2. Also, under the law, my must prove her major domicile in USA right?
My aunt currently has her primary address with me and I've been filing tax return with her under my name as dependent.

Thanks again.