I assume William and Joseph were brothers (same father's name at marriages) and also William gave place of birth as Fleetwood Lancs in the 1901 census. He stayed in the IOM until at least 1911, but brother? Joseph returned.

1911 census Findmypast household transcription:

Name, Relation, Condition /Yrs married, Se x, Age, Birth Year, Occupation, Where born

SALTHOUSE, Annie Wife Married 11 years F 35 1876 Ramsey Isle of Man
SALTHOUSE, John Son M 10 1901 Ramsey Isle of Man
SALTHOUSE, Joseph Son M 8 1903 Ramsey Isle of Man
SALTHOUSE, Robert Sumner Son M 6 1905 Fleetwood Lancashire
SALTHOUSE, Annie Daughter F 1 1910 Fleetwood Lancashire
RG number: RG14
Piece: 25458
Reference: RG14PN25458 RG78PN1455 RD477 SD4 ED3 SN233
Registration District: Fylde
Sub District: Fleetwood
Enumeration District: 3
Parish: Fleetwood
Address: 2 Church St Court Fleetwood
County: Lancashire

Annie wrote her address on the form as 2 High Street, Fleetwood, so I don't know where the address (above) came from. I will report it to FMP as a possible transcription error.
It had three rooms including kitchen. Annie wrote that she had had 6 children, 2 of whom had died.

Sue