Is the deceased brother considered a suicide and an unbeliever, or is he not responsible for what happened? And can something be done to reach him in his grave and be in the balance of his good deeds?

Since your brother's actions are unintentional due to illness, he is considered in the same ruling as an insane person and is not held accountable for them. We ask Allah to forgive him. You can benefit him by settling his debts to Allah and to people, by supplicating and seeking forgiveness for him, and by giving charity on his behalf.