Isaiah 51:19 has “these two things”; the Hebrew simply says “these two.”
On the other hand, 2 Nephi 8:19 has “these two sons,” who have the priesthood. These are the two witnesses, the two prophets in Jerusalem at the end of days, the time of Armageddon. John the Revelator also saw these two prophets.
John the Revelator’s Vision of the Two Prophets
Revelation 11:3
The ministry of the two witnesses or prophets in Jerusalem lasts for a period of 1,260 days (three and a half years). The number may be literal or symbolic. Three and a half is half of seven, the number of perfection or completion. Thus we understand that their mission is cut short.
Elder Bruce R. McConkie described their ministry in greater detail:
“Who are these witnesses, and when will they prophesy? ‘They are two prophets that are to be raised up to the Jewish nation in the last days, at the time of the restoration, and to prophesy to the Jews after they are gathered and have built the city of Jerusalem in the land of their fathers.’ (D&C 77:15.) Their ministry will take place after the latter-day temple has been built in Old Jerusalem, after some of the Jews who dwell there have been converted, and just before Armageddon and the return of the Lord Jesus. How long will they minister in Jerusalem and in the Holy Land? For three and a half years… . The Jews, as an assembled people, will hear again the testimony of legal administrators bearing record that salvation is in Christ and in his gospel. Who will these witnesses be? We do not know, except that they will be followers of Joseph Smith; they will hold the holy Melchizedek Priesthood; they will be members of The Church of Jesus Christ of Latter-day Saints. It is reasonable to suppose, knowing how the Lord has always dealt with his people in all ages, that they will be two members of the Council of the Twelve or of the First Presidency of the Church.” 14
Revelation 11:4–5
The prophet Zechariah also saw these two witnesses. He referred to them symbolically as two olive trees or two candlesticks (Zechariah 4:3, 11–14). Olive oil helps to heal, and candlesticks give light. The glory (“fire”) of these two prophets will be miraculously displayed in protecting them and destroying their enemies.
Revelation 11:6
The two witnesses will have powers similar to two of the greatest ancient Hebrew prophets: shutting the heavens so that it does not rain, as Elijah did (1 Kings 17:1), and sending plagues on the earth, as Moses did (Exodus 7–11).
Revelation 11:7–13
The two witnesses are killed, and their bodies lie in the streets for three and a half days, with nations viewing their bodies (perhaps via satellite transmission). Then they are resurrected and ascend into heaven while a great earthquake strikes the city.