Surviving Parent as Guardian
It is generally not necessary to name the other parent of a minor child as that child's guardian of the person. Of any two parents, the last surviving parent has the authority to nominate a minor child's guardian of the person.  Either parent must be living in order to accept the deceased parent's nomination, which also makes that person the last surviving parent.

It is more important to note that a step-parent does not automatically become the guardian of any step-children who are without a parent. If your present spouse is not the natural or adopted parent of any of your children, you must nominate that person if you would like him or her to serve.

See: Guardian, Who May Name; Guardians, Types