We don't know who they were. It was hinted in "Sky" (5 story) that Sarah Jane (and therefore the audience) would learn more about them later on but the death of Elisabeth Sladen put an end to that show. It's possible, of course, that we might eventually find out more in another show (such as Doctor Who itself) but there's no guarantee of that.
It's extremely unlikely that either of them could have been the White Guardian but, for all we know, they might have been working for him. On the other hand, they might have no connection whatever with the Guardians. We simply don't have enough information to say one way or the other.