Is selling shares immediately upon acquiring them—even though the company's activity is permissible, it deals with usury—valid, or must one dispose of the proceeds from their sale?

If the company deals with usury, both borrowing and lending, then it is considered a mixed company in which it is forbidden to invest, and the shares must be sold to dispose of the illicit gains. If the company genuinely transferred ownership of the shares to you in 2011 but prevented you from disposing of them for three years, then you must dispose of the profits generated from them during that period. However, you are not required to dispose of the original price of the shares. But if the company did not genuinely transfer ownership of the shares to you, but merely promised to do so, then you are not required to dispose of the price of the shares or their profits after taking possession of them, because it is a permissible gift, and the sin falls upon the company for dealing with usury.