According to the census he was born in ireland as was his sister florence.
No idea why except maybe work as they went back to pembrokshire however I havent checked birth records in ireland yet to make sure just took it for granted
This might be Florence's birth entry
Florence May SobeyDate of Registration: Apr-May-Jun 1892
Registration district: Cork
Birth Country: Ireland
Volume: 5
Page: 178
FHL Film Number: 101064
not sure about this one for Thomas
Thomas Henry SobeyDate of Registration: Jan-Feb-Mar 1895
Registration district: Inishowen
Birth Country: Ireland
Volume: 2
Page: 101
FHL Film Number: 101065
For info. - you may already have seen this
William John Sobey born 4 Dec 1889 Devonport, Devon
First Service Date: 12 Feb 1907
First Ship Served On: Ganges II
Last Service Date: 31 May 1916
Last Ship Served On: Indefatigable
Service Number: 238301
William John SobeyDeath Date: 31 May 1916
Cemetery: Plymouth Naval Memorial
Burial Country: England
Regiment: Royal Navy
Regimental Number: 238301
Ship Name: Indefatigable
Region or Memorial: Memorial Register
http://www.rootschat.com/links/01k2j/