I wonder if that is a rendering artifact. Does it change anything if you resize your browser window? Are you absolutely sure that you don't have any unintended partnership relationships? That might be worth double checking. I have a pretty similar situation, and it seems to render correctly for me. In the picture below, Peter is person 1, Derek is child A, Teresa is Person 2, Lori and Micky are child B, and Deborah is the sister of Peter (person 1). You can see that it is pretty correct when I click on Derek (child A).
Can you turn off last names and years and show us what you're seeing? You might have to use an image hosting site like imger.com so you can add your picture from the URL.