Do I need their SSN if I am the sole beneficiary of a life insurance and I want to divide the funds three ways which my sister wanted me to do?

It would be good to have those numbers. There may be tax documents you need to file. How you choose to distribute the life insurance to the other parties will determine if you are making a gift to the beneficiaries or if you are declining part of an asset that then gets returned to the decedent?s estate and distributed to the other parties.