They were at the same address - 54 West Port - not the same house/apartment/tenement ... the 1851 census shows that there were 62 people living at 54 West Port - looks like about 15/16 individual families/households - so they may not have known each other but certainly a coincidence that they both emigrated to Vic and at around the same time ...
(From his Aus death certificate I think my ancestor left Dundee in 1856 ... but he doesn't show up on any passenger lists ... very unhelpful of him!).
