well technically they are but they arent on the same side.
yes, they both want to save link, but oni-link is jealous of dark-link and her previous relations with him.
now for a trip to the past.
the whole reason dark link wanted to kill link in the first place is so she wouldnt have to tell him how she really felt. but dark link could never bring herself to kill him.
and little by little link became attached to those moments when he barely escaped with his life. and un-knowingly, link falls for dark link.
and oni-link is jealous of dark-link. so oni-link wants to kill dark link because she wants link all to herself.
and dark link is jealous of oni- link becaise oni-link is link's guardian, and is allowed to be close to him all the time.
so even though theyre helping link, they hate eachother
is that what you were asking?