Mutual Wills are different in that there is a binding agreement between the individuals to have their Wills in particular terms, which prohibits them from changing the terms without the other’s permission or after the death of the survivor. Mutual Wills are often identical in terms, but not always. They are common in couples involving blended families to prevent the survivor from disinheriting their step-children, if the biological parent dies first.
Mirror wills are identical in their terms. For example, a husband and wife who leave their entire estate to each other and then on the death of the survivor, to their children equally. These are the Wills commonly made by couples.