My fiancés father is deceased and his mother is remarried. My parents were never married, though I have my fathers last name. How should we word our wedding invitations?
You have several options, one example is:
Deborah LaFollette and Jerry Orrell
request the honor of your presence
at the marriage of their daughter
Sally Elizabeth Orrell
to
Scott Brian Holton
son of
Mrs. Mary Sparks
and Mr. Walter Holton (deceased)

