Hello! To "delete" your second set of parents, you need to go to "Set parents" again and click on the set of parents you want to remove. Instead of the parent's name, type in "(none)" and select this option. This will remove the parent-child relationship between the two people.
I don't think this site has the option to browse questions already answered. It is possible to search for tags (i. e. selecting every question tagged "siblings") but this is a quite broad approach, especially since a lot of questions aren't tagged.
Hope this helps!
