Yes, according to Islamic jurisprudence, it is permissible to marry your brother's ex-wife after she has divorced him, provided the 'iddah' period (waiting period after divorce) has been completed.
Islamic law permits marriage between a man and his brother's former wife after a valid divorce has taken place and the prescribed waiting period ('iddah') has been observed. The concept of marriage within Islam is based on consent and specific legal requirements, not on blood relations established through marriage. Because the woman is no longer married to the brother, no impediment exists for another man, including the brother of her ex-husband, to propose and marry her, provided all other conditions for a valid Islamic marriage are met.
The cited anecdotal evidence further supports this understanding.
