Affidavit of cohabitation

My friend has been very busy attending to her documents for the immigration the past weeks. She was requesting for my help regarding the legal papers that are being needed for their application with the immigration because of his foreigner husband. One of the requirements is the affidavit of cohabitation. It is a document where they state that they are living together as husband and wife for a certain period of time.  Also that they are known to the community that they are living together.  This is a notarized document so it needs a lawyer to affix the notarial zeal to validate its legality.