Hello Trisha
Here's another possibility to the "living in sin" bit. Perhaps there were 2 Hannah's! Mind, I do see that the Hannah who died in 1880 was the same age as the Hannah living with William in 1871! That is awfully coincidental

The birth certificate for Tom Justice Skelton would check the maiden name of that Hannah
2nd Quarter 1869 Horncastle Vol 7a page 512As for the Hannah English who married William in 1874, do you have her marriage certificate or just the note of it?
1st Quarter 1874 Stockton vol 10a page 104At least that would give her father's name and might help track her down.
Just a couple of thoughts anyway
Isobel