It seems that we share the same great grandmother. I too have struggled with finding this family and it was only when I looked under "Margaret Lumsden" that I found her in Scotlandspeople. Her father was Henry Lumsden not Henry Lumsden Bruce. I have put together some information on Margaret's family and I would be happy to share information. The "Bruce" is still a mystery to me and I haven't found any records of another marriage.
I also have tracked down Thomas Colledge who turned out to be Tuecke Colditz from Amrum Island in the North Sea (not Heligoland and not Bendigo - the Australian documents are misleading). I have a lot more information on this side of the family.