When a parent dies without a will can the adult children take possession of the deceased parent's property and assets in Oklahoma?

In order for the title to the property to pass to the heirs legally, at least one parent's estate (the last to die) must be probated. If there was no will then a member of the family must petition the court to be appointed the administrator. You should consult with an attorney who specializes in probate who can review the situation, determine how your parent's held title to their property and advise you on what legal proceedings must be undertaken.