Sponsor for B1 Visa

[redfan11]

Im a medical grad from India. I am applying for a B1 visa to appear for the Step 2 CS exam in june. i have a question regarding the sponsor. my father cant sponsor my trip as he is not very well to do financially. my maternal grandfather is the one who is sponsoring my education right now, but unfortunately he doesnt file IT returns. does this preclude him being my sponsor. his assets are quite sizeable(3-5 crores) would that help?
as a second option i have a maternal uncle who is also willing to sponsor my visit. He is a naturalized citizen in America.
i am employed and making around 3 lakhs per annum, but since i have started working a year ago i dont have enough savings to sponsor myself.
any advice regarding my application would be of immense help.
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[immihelp]

The person who sponsors you must have legal income on which he has paid income tax.

Black money can't be used to sponsor someone because that can't be shown on paper.