I've found that it depends on which individual you have highlighted. If you click on you, it will prioritize showing your parents. if you click on your wife, it will prioritize her's. If you click on one of your children, it will suddenly show both sets of parents. If you don't have children, I'd suggest adding an empty entry as a child and then edit out that box once you've downloaded the chart.
Hope this helps, I struggled with it, too. It's not at all clear.