Audrey,
I had to read your message several times before I could work out what advice you want! Assuming that your grandfather and second wife were of the right age to produce children, then you will have to check the birth records for Douglas from 1927 onwards. Are you certain that they didn't leave the Island?
Unfortunately, the records are not yet available on the Net and that will mean you visiting the Island (it makes for a wonderful holiday) or paying a researcher. Sorry, but there is no other way.
I don't have the Manx telephone directory with me, so I can't check to see if the surname is still present on the Island.
Good Hunting!
James