I found the family living in 1930 in Honolulu. John M. Cruz, head, b. HI, 48, house painter. Rebecca, wife, b. HI, 56. William, son, b. HI, 22. Pansy, adopted dau, b. HI, 6. Julia, adopted dau, b. HI, 2 5/12ths.
The 1940 Census is 98% indexed. You can keep track of it's status at familysearch.org.
John M. Cruz Born: Jan. 4, 1882, USA Died: July 3, 1968, Honolulu, Honolulu, HI Buried: Uluhaimalama Cemetery, Honolulu Source: findagrave.com
As you probably already know, vital records in Hawaii are restricted until 75 years after the event.
I'd look for John's obituary. There is a state-wide obituary volunteer at freepages.genealogy.rootsweb.ancestry.com/~obitl/volhi.html .Hopefully his parents will be mentioned in it.
I'd contact the Honolulu County Genealogical Society, www.rootsweb.ancestry.com/~hihcgs/ about what records you might be able to view on-line.If you can find his birth certificate, that will contain info about his parents.
Another place to contact is the Hawaii State Archives, 808-586-0313. You can do a Google search for their web site. Successful Searching!