It appears your mother and father held the property in joint tenancy title, and one of the rights to that form of title, is the right of survivorship, and she would have survived to your father's share of the residence, regardless of what his will states, as the joint tenancy title is a during life document, whereas a will is an afterlife document, and therefore is not effective against a right of survivorship, as your mother survived to the title to the whole property. Thereafter, she can make out her own will, and direct the will to pass the house to whomever she wants, and no signature is required from anyone.
Answered on Aug 13th, 2013 at 9:36 PM