Probate Beneficiary troubles?

I am the sole fiduciary for my Grandmother's estate. She passed about 1 1/2 years ago. My grandmother's will was set-up as discretionary trusts for my Dad and my Aunt with stipulations about distribution (although totally discretionary). My father has been really a pain in the *** to deal with on this. He fails to realize that all of her property passed into my possession as sole fiduciary. As the beneficiary he seems to think he has total control and I have been trying to tell him that because of the discretionary nature of the trusts, he actually has NO control of the estate and needs to back off. My only obligation to him is to distribute the funds as outlined in the will. He has side-stepped and gained access to some of the estate funds, but I have blocked him from gaining access to any more. I am getting so tired of arguing about this with my own Father... HELP!