Not related, but did a little "detective work" and got my eyes crossed in process with census records, but I believe answer is Caroline is Ethel's mother.No wonder you had question about it way they wrote it up on 1930 census-should have been m-in-law- ah the fun of it all. I find her on 1910 and 1920 census with husband Martin,(Martin and Carline married first at 35 and 25) living with or next to Charles and family. 1910 Onaway, Preque Isle County MI census lists Charles as son-in-law to Martin. Hope this helps. Good luck with your continued searches.

Looking for date of death of Caroline Swarthout Beebe. She was born 20 Oct 1858 in NY to Jonathan Swarthout and Caroline Phillips. She married Martin Beebe, 10 Jan 1875 in Greenbush, Clinton Co, MI

I last have her listed on the 1930 census is Forest, Cheboygan Co, MI living with her daughter, Ethel Beebe Bishop.

Thanks!
Maureen Garner Elliott