When you encounter the big mouth in the family, you will want to limit your conversation with such a person and try hard not to say anything to him or her that includes a name, place, or anything related to other family members unless absolutely necessary. When referencing your personal interaction with other relatives, you might be vague and only mention labels such as: "an aunt, a cousin or a relative" rather than names. Taking care to leave out any details that might be misconstrued and keeping private information to one's self.
If there is a confrontation or family dispute over what the big mouth relative said, stand your ground! Don't feel threatened, bullied, or curse the person you are speaking with. Rather stick to the facts and give the person or yourself a way out if the discussion because emotional. You don't want to keep conversations going with people who easily jump to conclusions, act childish, or have so many rules about what to say or not to say about them.