Charitable contributions, and corresponding deductions in the context of an income tax return for an estate, need to be expressly provided for in the decedent's will.
See https://www.irs.gov/publications/p559/ar02.html#en_US_2016_publink100099699
You might want to consider the personal and household effects as having been distributed to the beneficiaries and then the beneficiaries, in turn, having donated the items to the charitable organization (which will allow them to deduct their share on their individual income tax returns).
