Hello. I believe I can be of help to you with this issue.
It is impossible to diagnose someone over the internet like this. The symptoms and behavior you describe best align with something called a Personality Disorder. You can Google the following topics and then respond to me: DSM-IVTR Borderline Personality Disorder
; DSMIVTR Narcissistic Personality Disorder. It is most common for people with a personality disorder to have a mixed type of disorder rather than a single, 'pure' type. That is, they will have some clear signs of one disorder and signs of another; they may not show all signs of both disorders.
People with personality disorders have life-long, unstable relationships. They have deficits in the ability to experience true empathy for others and fail to see how their behavior emotionally affects others. They dishonestly manipulate others in order to extract all of the resources they can. They tend to constantly blame others when problems arise in a relationship and can never accept responsibility for their role in creating a relationship problem. They strike people as self-centered and self-focused, at the expense of other loved ones---they almost never truly sacrifice their time and material resources to help others, UNLESS they do so because it will bring them attention and and significant social recognition. So their motives for sacrificing and giving are still quite obviously selfish. These people also do not benefit from therapy because they truly believe there is nothing wrong with them; all relationship problems are due to the misbehavior or problems of others, so they cannot easily admit their personal faults and contemplate change. Only when a very serious emotional crisis occurs might they be vulnerable to the influence of therapists e.g., a spouse files for a divorce. There is virtually nothing a single person, outside of the family structure can do to get the person to change their behavior---it takes a joint effort by all family members to agree on how to handle the person's selfishness and hurtfulness. For example, there can be a common agreement about how family members will deal with damaging gossip or stories the person might spread about other family members.
I'll pause here and ask you to look up these personality disorder topics and then comment on this family member's behavior and personality style. There is a substantial time zone difference so we may not interact again with this question for many hours or perhaps, a day or so. I am willing to be patient in exchanging information, if you are.