Mutual Wills
Wills made by two or more people that cannot be changed unilaterally after the first death. Distinguished from Mirror Wills.
Mutual Wills bind the survivor: after the first death, the survivor cannot change their Will to depart from the agreed scheme. The agreement creates a 'constructive trust' enforceable against the survivor's estate.
Mutual Wills are problematic in practice: rigid, often disputed, and difficult to evidence. We strongly recommend Mirror Wills, which are independent, over Mutual Wills.