The will-makers are spouses or partners who agree to make their wills together in an agreed form.
The will-makers want to provide for one another but commonly at least one of the will-makers will have children from a previous relationship that they also want to provide for.
They are very happy to leave their respective estates to one another but only on condition that when the second one dies they will leave an agreed gift or gifts to the children of the first will maker to die.
The will-makers want to be certain that the survivor of them will not make a new will after the first of them dies leaving out the children of the first to die. But in fact nothing can stop the survivor from making a new will except the knowledge that the beneficiaries who lose their inheritance as a result of the new will can sue the estate of the survivor. Those beneficiaries will sue to enforce the contract.
So a couple wishing to have mutual wills end up with three documents, typically a separate will each and a contract legally binding each other and their executors.
There is a husband and his second wife. The husband has children from his first marriage. The wife also has children from her first marriage. The husband might say in his will “I leave everything to my wife but if she has already died then 50% of my estate will be divided between my children and 50% is to be divided between my wife’s children”. Correspondingly, the wife will might say in her will “I leave everything to my husband but if he has already died then 50% of my estate will be divided between my children and 50% is to be divided between my husband’s children”.
How do they know that the survivor of them won’t make a new will leaving everything to their children and leaving out their spouse’s children? The answer is that if it is appropriate in all their circumstances then they will also sign a contract between them in which they both either promise not to change their wills, or they promise that if they do change their will it will still include the gift to the other spouse’s children.
If the survivor of them does in fact change their will then the children of the first of the couple to die have a contractual right to sue on the contract for compensation.
If you want to leave your spouse your estate (or part of it) and be sure that on their death they will include in their will a particular gift to your children.
If you and your wife agree to look after one another’s children from previous relationships but you want to be sure that the children can legally enforce that agreement.
If you and your partner have these concerns and you are not concerned that you may never be able to change your will ever again!
If you want to give your children from your previous relationship the right to sue the estate of your subsequent partner if that partner fails to make agreed provisions to your children in his or her will.
If you are unable to come up with a better alternative out of all of the other estate planning strategies available to you.