A Radical forgiveness question, please help:-

I read the first few chapters of the book Radical Forgiveness advised by my dear friend Anindita and it really opened my eyes ,solve my issues with people who have hurt me. Infact i have no bitterness towards those people or think bad , which also help improve my physical pain which i have been having for past 20 or more years. I use it in my everyday life as much as i can.But my question how do i apply it on a person/persons who are not directly hurting me but my dear ones (like my sister,parents).Like my sister's husband and his mother who are hurting my sister without a break day and night. I do forgiveness for them but the next moment i get know something terrible done by them and i get hurt.I'm a very sensitive person and cannot see injustice on anyone. I get hurt immediately and my mind stays unsettled then for long.