A Mirror Will are used by couples whose intentions match each other. Whilst there are two separate documents, the Wills mirror each other (hence the name). However, you do not have to be married to create a Mirror Will.
Mirror Wills can be changed at any point by either party without the other person knowing, so a high level of trust is necessary when writing a Mirror Will. As such, in instances where children are involved it may be wiser to write a Trust Will to ensure that they remain as beneficiaries should you pass before your spouse.
It is again possible to cover funeral plans in a Mirror Will as well as electing to distribute more personal and sentimental items to loved ones.