What I did was from Robert's edit page on the right-hand side I clicked to edit father, then at the very bottom of the next page the big green button to remove Ellen as his father. Then I clicked to edit mother and removed Thomas. Then i clicked to add father and put Thomas' ID# in the first box provided and clicked to add. Same for adding Ellen as his mother. They both had the correct genders so there was no adjustment needed, but that could be done from the edit page of an individual profile.
I hope this helps, have a great day!