If a notary is a beneficiary in a document, or is related to someone who will benefit in some financial way from a document, then the notary has beneficial interest and should not notarize that document. Some other notary who is not involved in any way with the transaction or family members involved in the transaction should be chosen to notarize the document. Beneficial interest is similar to financial interest.
A beneficiary is somwone who will gain money or other benefits if a document is signed.