A joint will, also called a “mirror will,” “mutual will,” or “reciprocal will,” is a will that may be executed by a married couple to ensure that their property is disposed of identically at time of death. In a standard joint will, the wife and husband make identical wills that provide when one spouse passes away, the surviving spouse receives everything, and when both of them pass away, the estate would be left to their children or other beneficiaries. Except for your spouse, State law allows you to leave your estate to anyone and for the most part you are free to disinherit any family member.
The Sharī‘a, on the other hand, is a fixed share system. You have restrictions on the distribution of your estate. The Sharī‘a has certain gender-specific obligations and the inheritance rights of each spouse’s beneficiaries are different. For example, the parents of one spouse are not the legal heirs of the other spouse. The inheritance distribution of each spouse is also different. For these reasons, the Sharī‘a does not permit a person to leave his entire estate to the surviving spouse. For this fundamental reason, a joint will would violate the requirements of the Sharī‘a.