It's an interesting one... When I started the divorce process and then later (after the threats to kill, police, yadayada) made him leave the family home, I really started opening up about what had happened.
What I got, including from his actual family, was understanding and support. Because they had known all along. It was the same with my friends and my colleagues. There were two people who were not supportive: my uncle, whose first question was 'can the marriage be saved?', and my mother (not uncle's sibling) who was an alcoholic herself.
When it comes to people in the family, they will either blame you as the parent/partner (because that conveniently excuses them from doing anything!) or they will support you because they already knew and were too afraid to mention it.