How to find shares of stock?

I have numerous relatives that were involved in the Coca Cola Bottling business and I am sure they owned shares. My grandmother would be the last living relative but my grandfather and great grandparents were also owners. I asked Coca Cola investor relations but they just said to call their brokers and computershare to ask. Shouldn't they be able to provide information related to if my relatives even still own shares? I don't want those shares to get stuck in the infinity loop when my grandmother could be using them. Should I contact the Compliance Officer?

Thank you