Dear Mr. Underwood,
Thank you for posting your request on History Hub!
We suggest that you search Chronicling America: Historic American Newspapers and other newspaper indices for mentions of the marriage and/or death of Margaret Barnett and her family. Often obituaries will note the names and residences of other family members. Also, we suggest that you request a record search from Tennessee Vital Records, the Arkansas Department of Health, and the California Department of Public Health.
We hope this is helpful. Best of luck with your research!