More Update: Perhaps I should have been more explicit about the complete wrongheadedness of the sort of speculations which could be triggered by Archbishop Gaenswein's piece.
We believe in the Monarchia of "the one God and Father". That is to say: the Father is the arkhe, pege theotetos ... the source and fount of the Godhead which He shares with Son (by filiation) and Spirit (by procession). All Fatherhood derives its "Name" from him. So the Fatherhood expressed in each particular Church by the one Bishop is the One imaging and embodiment of the One Fatherhood of the One Father. This is as true of the Roman Church as it is of every other particular Church.
A literate Byzantine might be forgiven for wondering whether we Latins are really Dyotheists who believe in two Principia Deitatis.
Vide Ephesians 3:14 and 4:6 and the Epistles of S Ignatius.
We have quite enough doctrinal disorders floating around at the moment without 'traditionalists' inventing new heresies of their own.
ORIGINAL POST: Since someone has asked me, I will express the view that Archbishop Gaenswein did not mean to say that there were two popes; nor to say that the papacy subsists in two individuals.
There can only be one Pope, and that pope is Francis. There can only be one Bishop of any diocese, but when a Coadjutor is appointed, he does acquire a close relationship with the One, Single, diocesan whom he is assisting. But, at least until recently, coadjutors retained the titular see in partibus which they already had. Perhaps having an emeritus pope is a bit like being a coadjutor bishop. By the way, 'emeritus' does mean 'having given up the job'.
As I said at the time of the Abdication, I felt it would have been more appropriate for Joseph Ratzinger to be given some such style as episcopus ad Sanctum Petrum, rather like the auxiliaries to the Saxon Archbishops of Canterbury who had their Cathedra in the old church of S Martin and were styled episcopus ad Sanctum Martinum.
I am a little uneasy, frankly, about anything that gives any impression whatsoever that the Papacy is anything other than the bishopric of Rome. As Fr Eric Mascall pointed out, the Papacy is not a sacramental rank in the Church such as to confer an indelible character. The purely administrative act of electing a man Pope does not change him in the same way as the ordination of a man to the diaconate, presbyterate, or episcopate changes him. Being elected pope does not mean that through all eternity you will be, in some mystical mysterious sort of way, a pope. When you die or abdicate, you cease being a pope.
Joseph Ratzinger is not Pope; nor a Pope; not half a Pope; not in any sort of way whatsoever.