I just thought that I would mention this. I have been looking through a booklet written by my Grandfather. It’s a history of Brighton Mennonite Church in Chicago, which began as a mission under Abram F. Wiens and his wife, Katherine (nee Kroeker). Also inside is a mention of Katherine’s sister Sarah Kroeker, her work at the mission, and her marriage to Oskar Andersson. If you are a related to Oskar and Sarah, then you might want to look at it. E-mail me.
By the way, I’ve also seen on-line that there is a book about Oskar and Sarah - Oskar and Sarah: A Congo Love Story by Helen Neufeld Coon. (Don’t ask, I don’t have it.)