Complex sentence: Their feast day in the Roman Catholic Church is 19 June, the day of the translation of the relics; but in the Eastern Orthodox Church on 14 October (O.S.)/24 October (N.S.), the traditional day of their death.
Split into simpler sentences: Their feast day in the Roman Catholic Church is on June 19, the day marking the translation of their relics. In the Eastern Orthodox Church their feast takes place on October 14 (O.S.)/October 24 (N.S.), the traditional day of their death.