Get a copy of his birth certificate. This will give you the names of his parents.
Get their marriage certificate, which in turn will give you the names of their fathers.
By now you should have the names of people who would appear in the 1901 census and will probably give you other family information.

Certificates are available from the Registrar in Douglas, see
http://www.gov.im/registries/general/civilregistry/welcome.xml