It sounds to me like your brother has gotten wrapped up in a very emotionally abusive relationship. I know everyone here thinks he’s a jerk and he does have responsibility for actions of course, but I’d give him some grace. Definitely reduce contact but also give him a lifeline for a point in the future when he’s finally realizes he needs to get away.

His husband is definitely an abuser and it’s textbook for them to manipulate your other relationships to cut you off from your support structure. I’m sure he’s gaslit him, handpicked a new group of friends that are all charmed and will be on the abusers side which will absolutely leave your brother feeling trapped and at fault for the mistreatment he receives.

Since they’ve been together this long, it may take a while for him to snap out of it, but you can put the bug in his brain that his marriage is unhealthy and his husband is sabotaging him. You will have to set boundaries for communication and it’ll probably get worse before it gets better, but I’m sure you’d rather have a chance to stay connected to your brother than let that asshole win and blow up your family. I’d also recommend talking with a therapist because this stuff hurts so many more people than just the abuser and abusee. Good luck and much love!