People often make the mistake in their Wills of nominating a couple to be the guardians of minor children. It sounds like a good idea to nominate a husband and wife jointly, so that is what many people do. For example, someone might nominate their sister and her husband to be guardians.
The problem arises if the couple is no longer together at the time when a guardian needs to be appointed. The court has to determine what the deceased intended. For example, if the sister in the example passes away, the court has to decide if the deceased would have wanted the husband to still be the guardian. It is not an easy decision for a court to make because the parents cannot be asked.
The point of this is to get you to think about how you want to nominate guardians for your minor children. You can nominate a couple. However, when doing so, you should be clear about what happens if that couple is no longer together for any reason.