Legal Question in Wills and Trusts in Mississippi

The children of the deceased son will inherit an equal share of their father's estate under the law of intestate succession in Mississippi or whatever their father provides in his Last Will and Testament. They will not inherit any interest in the property if their father was a joint tenant with his surviving brother or if their grandmother had will designating someone else as a legatee for the property and the brother's only held the property as fiduciaries for their mother.