I realize it is a stretch, but when looking at the 1861 census for the family I see Fenton and Johanna are the same age. They are listed as Catherine's son and daughter and both married. My suspicion is they were married to each other and the census taker neglected to put "inlaw" by Johanna.
I also wondered if the person recording the wedding of "Franciscum Moore" and "Joannam Power" put Franciscum as a given name if it was the closest alternative to a Latin version of his name. If so, and that could be Fenton, Joanne BURKE of Salford was a witness at Fenton's marriage. Fenton's sister Oney/Ann Burke married John BURKE.
The Lan-OPC shows:
Marriage: 30 Sep 1860 Cathedral Church of St John the Evangelist, Salford, Lancashire, England
Franciscum Moore - Salford
Joannam Power - Salford
Groom's Parents: Joannis Moore & Catharinae Moore
Bride's Parents: Joannis Power & Catharinae Power
Witness: Joanne Burke of Salford; Birgitta Whelan of Salford