By reading online, I believe I have to file I-864 for my Dad's case as well as cosponsor right?
-Right if your aunt's income is not enough.
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.
-She can use your address as hers in US.
Thanks again.