Hi Mike
A very delayed reply, for which I apologise - why work has to get in the way of family research I don't know !!!
I wanted to let you know that I haven't notified LDS as yet because I've been checking details on the death certs of both Joseph and Susanna - paticularly where it lists children of the marriage.
Joseph died 1888 - 2 females living (Mary & Annie) 1 male deceased (looks like this was James Hepple Willis)
but on Susannah's d 1919 - Mary (65), Annie (59) living; 2 males and 1 female deceased.
Now I'm not so sure that Sarah Jane can be completely discounted
and who the other male could be I have no idea.
It's weird though that the 2 certs that were about 30 yrs apart have conflicting info regards the children of the marriage
Looks like I have further research to do on this one -:)