When I look at at the Detail page for once of my ancestors, he is in his correct family, but he is also attached again to just his father. How can I correct that?
Click on the edit button of your ancestor where he appears as a child with just his father. Next to the father's name click Remove or Replace. I click Remove and type Duplicate as the reason. Now your ancestor should appear only with his mother and father.
The most complete answer depends on the exact circumstances of the record.