coffee_black, get her and kids to a safe place. Remind her that it is more than her kids physical lives but emotional lives that are being threatened. Even if he doesn't kill her, what picture will that put in their minds and scar them.
Check with the authorities where she lives and where he lives. With recent events of family murders, they may be more receptive. Whatever tell her it won't get better without intervention, better for her and the kids. Don't bother worry about "saving" him.
In this area I know of 2 female jws that were threatened with a gun by their jw husbands and the elders did nothing. They were lucky that the kids called the police on one and the gun jammed on the other.
Call any battered women groups and they can help you better than we can...yes, WAC, there are many wackos out there that should be locked up.
Blondie