My mother passe away around 4 years ago and I am the trustee, I want to buy out my sister, is the home price based on today' or at the time of death?

The value of the house would be determined at the time of the sale, not at the time of the death. I suggest negotiating with your sister and come to an agreement on the price. Timothy C. Felice, Esq. Felice Trial Attorneys 561-444-8822 InjuryTrialAttorneys.com