My mother never knew with certainty who her birth father was. My widowed great grand mother remarried Olaf Matildus Pedersen LHX1-9RC. They had 3 children. My grandmother was a child of her 1st husband. Using DNA and 1920 records, I have connections to children of the 2nd marriage that are uniformly stronger than Shared cM Project 4.0 tool would suggest with a normal paper trail. The evidence leads me to believe that mother's biological father is my grandmother's stepfather. This fits with the verbal gossip in the family of the 1st family.
How is this accounted for when creating a family tree? The 3 children of the 2nd marriage are both1/2 siblings and 1/2 aunts and uncles to mother.
It was a messy situation in 1920.