You need to speak with a tax and estate lawyer for this. A lot of what happens after your grandfather passes depends on what relationship your mother has to the trust. Did she and your grandfather own the property together and place it in trust, is she just a beneficiary, or something else? Depending on the structure your mother could get a stepped up basis in the property with depreciation deductions disappearing or she could get the property with the same basis after your grandfather passes. Someone needs to be able to review the entire terms of the trust and that should be a local attorney who has knowledge of estates and trusts and real estate.
