Thanks for the info on marriage and divorce access being at the county level and not online. It sounds like I'll have to start with the known counties of residence and hope to find a volunteer or paid researcher to try to find them.
I do have his death certificate copy and he did die at the state hospital in Napa as you speculated. I also have his birth certificate from New Jersey in 1900. He would have been my late father's half-brother, who my father didn't know existed. So I'm anxious to learn of these marriages and especially if there were children involved.