Your question got cut off. Check the Latest Changes on the right hand side of the page to see where these names came from. Check the sources to see if they really are children of your grandparents. If not, then you may have to fix bad merges or unconnect them from your family.
Have a look at the change log ("Show all changes" section) on your grandparents' records. If it appears these were/are their children and (for some reason) they were attached then quickly detached from having a relationship, you can restore this.
If you need help, post your grandparents' ID references here. Assuming they are deceased, a more experienced user should be able to provide specific advice on your best options. However, there will be a problem in others viewing the details of anyone who is "living".
. . . note however - I am not aware of any "automatic adding" (to FamilySearch FamilyTree)
People get added by people going in an consciously adding them.
but as Paul points out - the Change Log - should indicate what happend and who did it.
Thanks for the replies