FIT
Fitbit, Inc. Class A common stock
stock NYSE

Grandma received royalty payment. Grandma owes tax (final return).
Wife received cash as of the date of grandma’s death.
Now tell me how grandma’s estate is paying the final tax. This is the point your CPA is making. FIT has to be paid from the estate assets prior to distribution. All assets are distributed post the final income tax. All heirs will receive net of tax. Depends on how the final income tax is allocated. Did grandma consider the tax liability?
I would suggest there is a real probability to assume all tax from your tax. THAT doesn’t seem to match. Probably allocate on share of taxable income for the year. Example, Social Security income benefited all assets, not just cash.

Grandma received royalty payment. Grandma owes tax (final return).
Wife received cash as of the date of grandma’s death.
Now tell me how grandma’s estate is paying the final tax. This is the point your CPA is making. FIT has to be paid from the estate assets prior to distribution. All assets are distributed post the final income tax. All heirs will receive net of tax. Depends on how the final income tax is allocated. Did grandma consider the tax liability?
I would suggest there is a real probability to assume all tax from your tax. THAT doesn’t seem to match. Probably allocate on share of taxable income for the year. Example, Social Security income benefited all assets, not just cash.