Repairing Family Relationships: Should Violence Be Used To Stop Violence?

(All names have been changed to protect the identities.) Sandra’s boyfriend Bill was kind, loving, and generous - until he lost his temper. Then he became violent. And he was irrational in his jealousy and suspicion. Sandra’s older sister DeeDee was a bit of a roughneck. She had a boyfriend Antwan who was known to be a bit of a thug. When Sandra called DeeDee crying and describing how Bill had beat her because he suspected she was cheating on him, DeeDee got enraged. She called Antwan, who got his boys together and confronted Bill as he was coming out of Sandra’s home. They gave him such a severe beating that he had to be hospitalized. Afterward, he broke up with Sandra and never came near her again. But now Sandra is angry at DeeDee for destroying her relationship. DeeDee feels that her little sister should be grateful for getting her away from such a man.What is the best way to intervene in a violent relationship?