Going by the information on the marriage details it says William Owen's place of birth was England.
Taking into account you felt his mothers names was Sarah Hudson
on the pioneer index for Victoria
OWEN Frederick Deshon Johannes Hampshire father William mother Sarah HUDSON
Born At Sea in 1872 reg no8132
OWEN Arthur Thomas died in 1872 birth place Norf
father William Owen mother Sarah hudson reg no 4038
OWEN Frederick died in 1872 aged 5 months AT SEA
father William Owen mother Sarah HUDSON
Now working from this information I found the family entered in Victoria on Board the vessell
"the Hampshire" in Feb 1872
http://proarchives.imagineering.com.au/index_search.asp?searchid=23William Owen was 32 , his wife Sarah Ann was 26 the children were unnamed infant 1 Arthur T aged 1 Frank H aged a Minnie J aged 5 and William E aged 3
kind thoughts Jenn