If you are now an official member of wikitree, you can go to the profile page of the child and go to the edit button located above. Press this tab and it will take you to the edit page On the right hand side, there will be links to the parents and siblings of child. You can add/ edit these links. Press add/edit of mother to add mother information and after entering information, be sure to save the information. You can do this also with the father and siblings of child.