Thank you for adopting some "orphans!"
At WikiTree, since everything is shared and likely connected to something or someone else, deletion is not something done often. The prefered methods are separating people if they are unrelated, or merging two or more profiles into one if they are the same person. In your case, you can go to your ancestor's profile, and use the edit tab to separate them from the incorrect children. On the right hand side there is a section for "Children" and a link to "Add/edit." From there, at the bottom of the page there is the option to remove children.
For the duplicates with spelling variations, you can merge multiple profiles into one. For more on merging, check out the Merging FAQ.