The Holy Father is assisted by Msgr. Guido Marini, his papal Master of Ceremonies. Msgr. Marini also heads the Office of Liturgies of the Supreme Pontiff. There is another priest assisting him during these Papal Masses. I do not remember his name, but, he is also an official with the Secretary of State’s office.
There are two deacons who assist the Holy Father during the Mass. One is the Deacon of the Gospels (he carries the Book of the Gospels) while the other is the Deacon of the Altar (I think that is the term) who assists the Holy Father during the Liturgy of the Eucharist. Now, it does get somewhat complicated because in previous high holy days, two Cardinal Deacons flank the Holy Father. These are Cardinals who, although they wear the mitre, are vested in the deacon’s dalmatics. I was surprised to not have seen them for the Christmas Mass and the Urbi et Orbi Message and Blessing.