sorry for your loss. more importantly, is the cost reported the fair market value on the date of death (except for any acquired after he died)? thats the tax basis your mother assumes becuase she was not an owner when he died (not on the account)
for the date acquired held on the date of death you need to enter "inherited" no quotes
that tells Turbotax all the gains and losses on these securities are long-term. entering his date of death might not do this if it's less than a year between death and sale.
reporting type would be E "proceeds but not cost reported to the iRS" for cost you enter the FMV on the date of death. go back to the broker and request this info if you don't have it. Hopefully they'll be helpful if you give them the reason.
IRS instructions say use code B and enter zero in adjustment column
