My grandfather told me that he was leaving part of his estate to me. After my grandfather died, my father took control of all his assets and told us that there is a family trust. No will was found. Should we just assume that everything was left to our father, despite what our grandfather said?
If grandpa left no will or trust doling out some property to you and your sibling, you may be out of luck. If your grandfather's trust says so, your dad may be legally entitled to all of your grandfather's property.
Your best recourse here is to sit down with your dad and explain that your grandfather said you would inherit a chunk of his estate. Remind him that he has a legal duty to file a will, if any, with the local probate court (even if probate isn't required) and that if you are a trust beneficiary, you have a legal right to see the trust document. (In some states, you are also entitled to see the trust if, under state law, you would inherit in the absence of a will.) If you get a copy of the trust or will, pay close attention to your rights under it. If you can't decipher it, see a lawyer.
For more information on family members' rights to inheritance, see Inheritance Rights.