If there are two beneficiaries and one dies previous to the insured do proceeds go to the surviving beneficiary or half to the dead beneficiary's heirs?

There is no single answer to your question because the facts may be different in different cases. First, the insured should change the beneficiary designation if a named beneficiary dies before the insured's death. That will avoid problems later.

A beneficiary designation may include additional instructions when two or more beneficiaries are named. First, the insured can name "contingent" beneficiaries who will take a deceased beneficiaries share- on any life insurance policy. Second, the beneficiaries may be named as beneficiaries "per stirpes" or as "joint with the right of survivorship" where if one dies their share passes to the Survivor.

You need to check the designations on the particular insurance policy, the policies of the particular insurance company and the laws in your jurisdiction.