He specifically names Peter, Paul, and John.
Here is a portion of a prayer from St. John Henry Newman for the faithful departed:
May the heavens be opened to them, and the Angels rejoice with them. May the Archangel St. Michael conduct them to Thee. May Thy holy Angels come forth to meet them, and carry them to the city of the heavenly Jerusalem. May St. Peter, to whom Thou gavest the keys of the kingdom of heaven, receive them. May St. Paul, the vessel of election, stand by them. May St. John, the beloved disciple, who had the revelation of the secrets of heaven, intercede for them. May all the Holy Apostles, who received from Thee the power of binding and loosing, pray for them. May all the Saints and elect of God, who in this world suffered torments for Thy Name, befriend them; that, being freed from the prison beneath, they may be admitted into the glories of that kingdom, where with the Father and the Holy Ghost Thou livest and reignest one God, world without end. Come to their assistance, all ye Saints of God; gain for them deliverance from their place of punishment; meet them, all ye Angels; receive these holy souls, and present them before the Lord. Eternal rest give to them, O Lord. And may perpetual light shine on them. May they rest in peace. Amen.
From Prayers, Verses, and Devotions, published by Ignatius Press.
The saints tell us what Purgatory is actually like