Hello, my name is ***** ***** I will be the immigration attorney helping you today.
Actually, even if you extend your parents' E2 visa, as soon as your parents receive their green card, your brother's dependent visa would essentially be canceled. It is only valid as long as your parents have the E2. So it would not really matter if you had extended the E2 visa first. It would not help. However, If your brother is in the US, then he can go outside the US to a US consular or embassy to apply for the F1 visa directly. Then he can return with the F1 visa to the US and that would solve the issue.
Good luck to you during this process and I hope this answer has helped you!
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