E2 treaty investor visas cannot be "converted" to another category or to a green card. It is a "cul de sac" as many of my French clients like to refer to it. A "sibling's sponsorship" is fine, but takes six between 14 years to materialize and come to fruition. May you all live that long!
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Sibling's F4 category visa priority moves rather slow. It take about 14 years from the date the sibling properly files the application, for the visa interview to happen or adjustment of status to become ripe for filing.
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