No. After a person dies, their assets belong to their “estate,” not yet to the heirs or beneficiaries. Even though the heirs have possession of the assets, they do not have “marketable” title to the deceased person’s assets. Marketable title is achieved in probate. The Executor has no official power until the court has admitted the Will to probate and the Executor has taken an Oath. After appointment, the Executor can legally transfer title to the beneficiaries, which gives them marketable title.
For example, institutions like banks, stockbrokers, and title companies generally require Letters Testamentary from the Executor named in a Will before those institutions will release large sums of money to beneficiaries or allow the sale of real estate.