How does this work? (Dee)

I am estranged from my sisters, because they prevented me (lock and key) from seeing my mother during the last few years of her life. (I don’t know their reason.) The fact that they could treat me so badly makes me completely distrust them. I am trying to understanding and believe that a relationship is just what you think about another person. Can you have a relationship where this is no trust? How does this work?