Hello.....I am very sorry that your brother has suffered with this abuse for so many years! How awful. And indeed, the JWs often encourage people to stay with abusive spouses.
Oh, and before I go further, I should mention that almost everyone one on this site is EX-Jehovahs Witness.
While JWs believe that marriages should stay together, they will tollerate separation or divorce in cases of abuse. They may encourage the victim to stay, but if the victim chooses to go, the JWs will not disfellowship the victim for that.
However, the victim is NOT free to re-marry unless their ex-spouse sleeps with someone else. Period.
My mother left my abusive father. The JW Elders didn't like it, but accepted it. However, she could NEVER remarry someone else (Dad would never tell her if he had been with someone else...so 'in the eyes of God' the JWs believe the marriage is still binding.) She lived like that for some time and then one day decided to get married again. The JWs disfellowshipped her.
Tell your brother he is not sinning by separating from this abuser....even by JW rules.
I am sure someone will come up with some documentation from the JWs that you can show him to ease his mind.
You will need that: JW documentation that it is ok to leave an abuser.
-LisaBOBeesa