I inherited social security benefits from my father after he passed in 2016 and they were paid to me in full in 2018. How should I go about filing this?

He never received any of the money and it was split in 2 and paid out to me and my sister in 2018. I was not the Executer of his Estate. My name is on the form and it is an SSA-1099. In the bottom left box labeled Description of amount in box 3 it only says benefits for 2018: $(amount)
Is this considered a lump-sum social security payment before 2017? If so it asks for specific information from tax forms that I do not have because these payments weren't originally paid out to me.