I don't accept my brother as trans.
You do not think it is normal for someone to want to be transgender?
No, I don't think people can change their gender.
It's completely inappropriate to not accept your brother because he's trans. You should not discriminate against anyone because of their sexual or gender identity.
I'm not trying to be a dick but I want him to be a man. If you can change your gender, it means you can change sexual preference and become a gay.
While it may be difficult for you to understand, this is the decision that would make your brother more comfortable. Just know that if you do not accept him for who he is then you will never be able to have a lasting relationship with him.