Parks' nieces and nephews say Elaine Steele, who runs the Rosa & Raymond Parks Institute for Self-Development, influenced Parks to sign a 1998 will, the Detroit Free Press reported.
One complication is that no one really knows what Parks' estate is worth. When she died last year, suffering from dementia, most of what she left was personal belongings.
An auction house is trying to set a monetary value on items like a plate Parks used during a meal with former President Bill Clinton.
Parks was arrested Dec. 1, 1955, when she refused to give up her seat on a bus in Montgomery, Ala. The bus boycott that followed helped kick off the civil rights movement, and made a young minister -- the Rev. Martin Luther King Jr. -- into a national figure.