I am working on the Knisley branch of my family tree, and I have come across a conundrum of sorts. My great grand uncle, Ross Abram Knisley, was listed on the 1920 census as the son of John and Marguerite Ralston, both of whom could not be his parents as I have his birth record. He is the son of Harvey Knisley (died 1914) and Elizabeth Ida Bush (I cannot find her death date). Further complicating things is his obituary from 1977, which lists two living half-siblings, one of whom is Kline Ralston.

I would assume Ida remarried John Ralston after her first husband's death and then she died before 1920, then John remarried and listed his new wife on the census. However, when I look up the birth records of his half-siblings from that census, their mother is the same one on the census. Therefore, they did not remarry but stayed married the whole time. So I'm left again at how they could be his half-siblings unless there was an affair or something?

If there is anybody out there that knows something about this story and can clarify, I would be eternally grateful!