In the event that the decedent has failed to file a declaration or has filed an incomplete declaration for the property requiring a declaration by the Act and where the decedent meets the situation described under Paragraph 1, Article 7 of the Act, the beneficiaries shall be held liable for said failure to file a declaration or for the shortage or omission in the declaration and shall be responsible for making the tax and interest payment in proportion to the property they have each received provided the payment is within the total taxable estate or gift amount .