A notary public who has a direct or indirect financial (or other beneficial) interest in a document may not notarize such a document. The better practice is not to notarize for a spouse or family member in order to preserve the integrity of the notarization and to prevent a challenge to the notarization.
The only exception known to this rule is that you can sign on behalf of someone else as an Attorney in fact. You must have a signed and notarized Power of attorney to do so. You will sign your name and note below: “Attorney In Fact OR POA”
