Use these instructions to enter 1099 B. Remember you only report the capital gains after you sell the stock and the basis will be the value of the stock on the date of their death.
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To calculate the FMV of the stock on date of death, it is the average of the highest and lowest selling price of the stock on that date. If the stock traded at a high of $55 and a low of $53, then the FMV for tax purposes would by $108/2 or $54 per share.
If by chance the estate had to value the stock for the estate's purposes, you would use the value the estate used.