Especially on the death certs in CA that people were born a long time ago, the only info on the death certs were the info that living relatives provided.That would explain why some people died and are listed on the index, but (especially females) their parents last names are not listed.
In your case, I would think that Elsie was b. a Stuart (her father' last name was Stuart), however, her mother's last name was GRUNDY. MMN or Mother's maiden name is how that is listed.
If Otto and Elsie had children born in Cal after 1904, the children would prob be listed in the cal birth index.I did try a run for you with Clavel as father's last name and Stuart as mother's maiden name (for Elsie) and came up with nothing.Maybe you should run Clavel, with Grundy (as mother's maiden name).Even though it is not accurate, those records only rely on the people who were alive at the time and what they remembered.
You can run the Cal Birth Index with limited info and I encourage you to try various info in your searches.
Also...Do you think Kenneth Stuart was Elsie's brother or nephew?His birth date might help in trying to find him.
If you think he might still be alive, try www.switchboard.com (free internet white pages of the telephone directory).You can run his name and enter any state or no state.
If you are really trying to find him, think he might still be living and have a birth date or something, there is a service you have to pay for that searches voter registration and other databases for about $40 a search.
I'm just an amateur genealogist, but if you have more questions or info, please email me at firstname.lastname@example.org and I will try to help you.