Apostle Nathanael
According to the synaxarion, Nathanael was from Cana of Galilee and was brought to the Savior by the Apostle Philip. His name is interpreted as 'the gift of God,' and Christ identified him as 'a true Israelite,' a phrase the tradition glosses as 'one who sees God.'
Orthodox tradition identifies this Nathanael with the Apostle Bartholomew; the OrthodoxWiki entry for Bartholomew states that he is believed to be the same person commemorated on April 22 as Nathaniel of the Seventy.
Apostle Apelles
Apelles is numbered among the Seventy Apostles and is remembered as a figure who labored to spread the Gospel; according to the OCA account his missionary work led him to Rome, where he became a support for the faithful, and he is named in the Epistle to the Romans among those whom the Apostle Paul knew.
Sources differ on his see. The list attributed to Hippolytus names Apelles of Heraklion as bishop of Smyrna, while OrthodoxWiki, following the Prologue of Ohrid, places him as bishop of Heraclea in Trachis and records that he assisted the Apostle Andrew together with Urban, Stachys, Narcissus, Amplias, and Aristobulus. He is also commemorated individually on October 31.
Apostle Luke (Loukios)
The Luke of this commemoration is Loukios (Lucius) of the Seventy, who is distinct from the Apostle and Evangelist Luke. He is numbered among the Seventy and, according to OrthodoxWiki, is greeted by the Apostle Paul in Romans 16:21.
He served as a bishop; the Hippolytan list identifies Lucius of Cyrene as bishop of Laodicea in Syria, and OrthodoxWiki records his episcopate at Laodicea. His principal feast falls on September 10, and the OCA also commemorates him on January 4.
Apostle Clement
Clement is numbered among the Seventy Apostles and served as Bishop in Sardis, as recorded by OrthodoxWiki and reflected in the Hippolytan list, which names Clement bishop of Sardice (Sardis).
Besides the April 22 commemoration with Nathaniel and Luke, he is remembered on January 4 with the Synaxis of the Seventy Apostles and on September 10 together with Apostles Apelles and Lucius.