Concelebration of Priests, Permanent Deacons and the Extraordinary Form of the Mass:
Is concelebration among priests allowed in the EF Mass?
Concelebration does not take place in the EF, except in the following very specific situations: the ordination of a priest and the ordination of a bishop. The only priests who would concelebrate at the ordination of a priest are the celebrant and those who were ordained at the Mass.
Yes. A priest, though ordained to a higher order does not “forfeit” the lower orders he has received.
Yes. It is not uncommon to have a Solemn Mass with an ordained Deacon, whether transitional or permanent serving as the Deacon or Subdeacon. Additionally the Eccclesia Dei commission granted permission to instituted Acolytes to serve as Subdeacons at the Solemn Mass, with the exception that they cannot wear the maniple or wipe out the chalice after the ablution.
May priests vest and function as deacons and subdeacons?
Can permanent deacons serve as deacons and sub deacons in the EF Mass?