JOEL - Elias:
In D&C 110 both Elias and Elijah are reported to have appeared to Joseph Smith and Oliver Cowdery. Critics claim Joseph Smith made a mistake in not knowing that Elias is the Greek name for Elijah. However, Elias is both a name and a title and has four meanings:

(1) The Elias that appeared to Joseph Smith and Oliver Cowdery was a man, of Abraham's time, who "committed the dispensation of Abraham" which included the blessings of God's covenant with Abraham to the Prophet Joseph Smith and Oliver Cowdery on April 3, 1836, in the Kirtland Temple (D&C 110:12 )

(2) "Elias" appears in the New Testament as the Greek transliteration of the Hebrew name Elijah (e.g., Matt. 17:3 ; James 5:17-18 ).

(3) A forerunner in building God's kingdom is called "an Elias" (Teachings of the Prophet J. S., pp. 335-36).

(4) A prophet who helps restore something of particular importance is also referred to as an "Elias" (JST Matt. 17:13-14 ).

In scripture, therefore, the name Elias may refer to a preparer, a forerunner, a restorer, to Elias himself, or to Elijah.
Individuals who have acted as forerunners or restorers include Jesus Christ (JST John 1:21-28 ); Noah as Gabriel (D&C 27:6-7 ; TPJS, p. 157); John the Baptist (Luke 1:17 ); John the Revelator (D&C 77:9, 14 ); Adam as Michael, Moroni2, and Peter, James, and John (D&C 27:5-13 ; 128:20-21 ); and Joseph Smith (D&C 1:17-18 ; TPJS, p. 335). Each of these may be considered an Elias.
Therefore Elias(#1) and Elias #2(Elijah) both appeared to Joseph Smith and Oliver Cowdery.

Esaias:
Esaias is the Greek form of Isaiah, yet in D&C 76:100, Joseph Smith distinguishes Esaias from Isaiah:

"These are they who say they are some of one and some of another--some of Christ and some of John, and some of Moses, and some of Elias, and some of Esaias, and some of Isaiah, and some of Enoch;"(D&C 76:100)

Another mistake by Joseph Smith? No.
In D&C 84:11-13 we read of an Esaias who was a prophet who lived in the days of Abraham, many centuries before Isaiah.

"And Gad under the hand of Esaias;
And Esaias received it under the hand of God.
Esaias also lived in the days of Abraham, and was blessed of him—"

So in the D&C 76:100 verse Joseph Smith was talking about another person named Esaias, not mentioned in the Bible, separate from the Isaiah of the Bible.