Is it permissible for my brother to marry a woman if he informs her of his condition, taking into account that he lost both testicles, is taking male hormones, and is inclined to be a female?

What is understood from the question is that your brother is a man, and he has developed delusions and corrupt ideas due to losing some of his male organs in his early youth, which made him imagine that he is not a man but a female. This, in addition to a lack of proper upbringing and awareness, and what solidified this idea in his mind was what was inspired by human devils and embellished by corrupt doctors.

We advise the brother to fear Allah Almighty and to stay away from thoughts of suicide or anything else. He must repent to Allah and start a new life based on piety and righteousness. You should help him with this, and go to sincere psychiatrists, and connect him with righteous and upright people, the company of the righteous, and gatherings of good.

There is no religious impediment to his marriage; in fact, marrying a righteous woman may be one of the means to his healing and solving his problem, for his loss of some of his organs does not remove him from the ruling of masculinity. Malik said in Al-Mudawwanah: "It is permissible for a eunuch to marry and divorce." He must inform the woman he wishes to marry, especially if he is unable to have intercourse.