Reg B Appraisal Rules and CFPB Mortgage Liens

We are a small community bank operating in a predominantly rural community. In many instances, we may have multiple mortgages on a dwelling, cross-collateralized across a customer's loan portfolio. In determining compliance for the CFPB Mortgage Rules, there are several references to first-lien transactions, Reg B Appraisal rules for instance. If our bank is the only secured creditor with multiple security instruments, are all of the mortgages considered the first-lien or is the first-lien the earliest dated mortgage and all subsequent mortgages are considered junior liens?