We need to avoid using the terms "will" and "probate" interchangeably. The two books mentioned contain abstracts of wills, not abstracts of probates. The individual in question may have died intestate, without leaving a will. His estate would still be probated, but there would be no mention of the probate in the two books mentioned. There would, however, be other probate documents such as an inventory and an administrator's account. The Lancaster Co Historical Society can tell you if such documents are available and can make copies for you. They may or may not specify the names of the heirs. There may also be deeds and/or Orphans Court records associated with probating the estate. These are more likely to contain the names of the heirs.