They do not need to be notarized. The author can simply write that they swear that the above statements are true and accurate to the best of their knowledge. Sign and Dated.
"Each affidavit must contain the full name and address, date and place of birth of the person making the affidavit, his or her relationship to the petitioner of beneficiary, if any, and complete information and details explaining how the person acquired his or her knowledge of your marriage." I-130 Instructions.
Andre Olivie, Esq.
Seattle Immigration Lawyer