Allah, The Most Merciful, The Most Compassionate never created a human being forced to do something which is clearly forbidden by Him. He mentioned in Quran and previous holy texts the sever punishment of people of Sodom when they insisted on their evil practice despite the teaching of their Prophet Lut (AS).
It is false and wrong to claim that this act is not a choice. It is in fact a desire like the desire of fornication or adultery or any sinful sexual desire. There are people who have sexual desires towards married women or to their own real sisters or even towards animals. It is simply an evil desire which can never be justified.
If your brother believes in Allah, then how can he understand the sever punishment mentioned in Quran ( Sura Hood, verse 82) and ( Sura al-Hijr, verse 74) on those who used to do similar acts.
You need to talk to your brother and remind him about the facts mentioned in Quran and by the Prophet (SAWA) and Ahlul Bayt (AS). You may take him to trusted scholars who can explain to him that desire is not a destiny especially when it goes against the clear and essential facts of Islam and morals.
If he applies his intellect and think properly, he should then realise the truth, but if he refuses the truth and insists on evil desires, then you can not help him as he is not willing to help himself. Nevertheless, you should not lose hope any way. Keep on trying to explain to him, as well as praying to Allah (SWT) to guide him.