Hi Brigcs
Gee, that's a sad story, but very intriguing at the same time - what a bit of luck having connected to the Aussie Calland-Scobles though. And the names must be a nightmare to look for!
CALLAND, CALLAND-SCOBLE, CALLANDS, SCOBLE, HAMMOND, H/Ellen H/ellen Marie???
I'm afraid I can't think of anything positive to help only ask questions!
I imagine you've considered, if she didn't die around time Vernon born, that she may have reverted to her maiden name. Have you gone the (expensive!)route of checking all deaths and poss re-marriages for a likely Ellen?
When Henry remarried, did his marriage record state he was a widower or divorced?
When did he arrive in Australia? Was the passenger list checked for Ellen?
Have you tried to track any of her other siblings besides Frederick, whose children you mentioned above, (as I can see on Census 1881 - Elizabeth, George, Bertha, ALbert ) their descendants may have heard a tale handed down as to what became of "Aunt Ellen".
Was Vernon born at home, or in a hospital - if the latter could records survive that may or may not mention Ellen if she died at that time?
Well, again sorry I can't be more help, but hopefully someone on RC may be able to pick up the baton.
BTW, on Genes Reunited there are 3 others listing Ellen HAMMOND 1874 of Walkern - are you in contact with them? And there is 1 listing an Ellen HAMMOND 1874 London... And there is Vernon's seaman's record in the National Archives too?
All the best
AMBLY