My Father Has Just Passed Away And I Am The Sole Beneficiary. His Half Brother Is Trying To Cause Problems. Please Help

Hello, I'm (29F) not sure how to start this or even what to ask, but any advice is very much appreciated. I just found out that my father has passed away. I am the sole beneficiary. I do not want to come across as disrespectful, but I don't know how to properly explain my situation. My father and I had a very strained relationship, he did not sign my birth certificate or pay child support growing up. He lived in California and I live in Ohio. Most of our relationship was communicating over the phone. I only saw him a few times in person. He had substance problems but he was in rehab and working on bettering himself. His half brother is living on the streets and has substance abuse problems and my father hated him. It is stated in his will that he is to get nothing. His brother has already contacted the executor of his will and the funeral home lying stating that he is next of kin and that I'm not his daughter and that he doesn't have one (The executor knows this isn't true and is the person who contacted me). He is trying to cause as many problems as he can and from my understanding everything he wants to do goes against my dad's wishes. My dad wants to be buried next to his father and brother who passed, but his half brother wants to cremate him and have him put somewhere else. He's also trying to go after everything my father had. I'm not sure what to do here. I don't know how to handle any of this. I don't know how to process any of this. Any advice would be appreciated. Thank you.