Since this property was owned by your mother's trust, the sale of the home is already included on the beneficiaries' Schedules K-1.
Keep Form 1099-S for your records. Do not enter the home sale again, or else reporting the sale would be duplicated.
The reason why the basis of the home is the same between the date of death and the date the home sold is because of a tax rule your accountant handled for you. It is a very good for you and the other beneficiaries. It is called "step-up" in basis. It means that the property is valued at its appraised value, which would have included the improvements.
