Is it permissible to marry a woman who was previously married by a guardian other than her father, given that her father had refused to marry her off, and intercourse had occurred with her, then she married another man and was divorced from him, knowing that her father does not speak to his daughter or spend on her, and is it permissible for her brother to be her guardian, given that the father might resent me because of what happened previously?

Firstly: If the father refuses to marry off his daughter to a suitable suitor whom she has accepted, without a valid reason, the guardianship transfers to the next in line among her guardians. If all of them refuse, then the guardianship falls to the Muslim judge, or whoever acts in his stead, such as the imam of an Islamic center. Otherwise, a just man can marry her off with her permission.

If the marriage took place in this manner, it is valid. Your separation from your wife without a divorce is not considered a divorce, and her subsequent marriage would be invalid. She is your wife now and does not need a renewed contract.

However, if the guardians other than the father did not refuse, and a foreign man married her off to you, then your marriage is considered فاسد (irregular/corrupt) by the majority of scholars. It is more prudent to divorce her to rectify the situation, especially if the marriage was officially documented. If you do not divorce her, then her subsequent marriage would be valid, because the first marriage was فاسد.

Secondly: It is permissible for a brother to marry off his sister if the father delegates him to do so. If the father delegated the matter of marriage to his son and asked him to communicate with you, then there is no harm in marrying her; in fact, it is preferable if she is religious and of good character.

It is not expected that any harm will befall your daughters as a result of this action, because "no bearer of burdens will bear the burden of another."