My step sister did not perform her duty as my father's executor of his estate ans she recently passed.

My dad died 3 yrs ago and his will stated that my nephew, step brother, step sister and I get his possessions. My stepsister got the house. She never sent anything to any of us. My s. brother and nephew got a copy of my Dad's will from me in Nov 2017 a month after my step sister died. She did not do her duty as executor of my Dad's will. My s. sister died Oct 21, '17 and she gave the house and it's contents to a friend. These people have had almost four months access and they have taken things from the house that may belong to us. Our family members were there on Sun 14, '18 getting what they allowed. The current executors were present and denied access to rooms and sequestered items from them. I believe that we need to sue my s. sister's Estate for breach of fiduciary duty, or whatever it may be called. We need help.