No. The cost basis is the FMV on the date of your mother's death*; not Jan. 2018 when you finally got ownership. This assumes your mother died after your father.
* Where the decedent's executor makes the alternate valuation election, then basis will be determined as of the date six months after the date of death (or, if the property is distributed or otherwise disposed of by the estate within the six month period, the date of distribution or other disposition).
