Generally it is the personal representative that files the form for all of the decedent property but there is provision that a transferee can file when property was not included in the form filed by the representative.
From the instructions or who must file:
"The transferee of property, if no personal representative
is appointed or if the personal representative does not
file a return, or if the personal representative files a return
but does not include the subject property. A "transferee"
means any person to whom a transfer is made and includes
legatees, devisees, heirs, next of kin, grantees, beneficiaries,
vendees, assignees, donees, surviving joint tenants.
The return must disclose any property or any interest
therein or income therefrom in possession or enjoyment,
present or future, in trust or otherwise which passes ownership
to the transferee. A separate transferee return is not
required for property included in a personal representative's
return. The inclusion of property in the return does
not constitute an admission that its transfer is taxable."
If the annuities represent a return on an investment (a single premium was paid), they are taxable and should be reported on REV-1510 Schedule G of the REV-1500 Inheritance Tax Return - Resident Decedent. Annuities do not qualify for the $3,000 exclusion allowed for transfers made within one year of the decedent's death.
Unless the decedent's Will provides otherwise, the inheritance tax is generally payable out of the residuary estate by the personal representative of the estate. If the personal representative does not pay the tax, the tax must be paid by the recipient of the residuary estate.
So, the grandson can but usually does not file the return and pay the inheritance tax.
Please ask if you need more discussion or clarification.