When the Acquisition Date and Cost Basis are blank, the broker that issued the 1099-B doesn't know these values.
You don't need an exact Acquisition Date; choose 'Inherited' in TurboTax for how you received the stock, and the holding period is automatically long-term. You can enter the date you got the stocks.
If you know the date of death, you can look up the historical value at Big Charts.
@Chuck48