Who were the Ezrahite brothers, Heman and Ethan,
authors of Psalms 88 and 89 respectively?

The Tapestry of the Levites
Three branches of Levi's family.
The priests, Aaron's family, also come from Kohath.
The figues in brackets indicate the number of generations.*

There are two main contenders. By far the most popular are the Ethan and Heman who were contemporaries of David, lead singers from amongst the Levites, descended from different branches of the same Levitical family. Ethan** comes from the branch of the Levites descended from Merari (concerned with the boards,bars and bolts of the Tabernacle, Num.3.35-6). Heman hails from Kohath, the branch from which Moses and Aaron also came. Heman headed a large family of 17 children, 14 of whom, his sons, occupied 14 out of 24 courses in the inspired and Divinely ordained arrangements for singing in the Temple. Both are described as Seers (those who perceive) 1 Chr.25.5, 2 Chr.35.15, and who prophesy 1 Chr.25.3. These would qualify them well to write psalms, as also did their much more famous contemporary Asaph, who coming from the third, Gershonite branch of Levi has his name to 12 psalms.

However there are strong reasons to hold this assertion in reserve.

Why are they both in the superscriptions to the psalms called Ezrahites? An Ezrahite (pronounced Ezrachite) is generally regarded as being derived from Zerach (properly) or Zerah, a patronymic. But where is Zerach in their genealogies? There is indeed a Zerach in Asaph's genealogy, 8 generations before, counting inclusively as is customary, but not the other two branches. So why would they be called by his name? Zerach means the rising or the dawn. It doesn't seem to be descriptive or titular, although some Jewish translators have translated the term 'native' or 'Israelite'.

The other aspect of the superscription in Ps.88, is to the 'Sons of Korah', also found in 10 other psalms. Does that mean the writer was of the sons of Korah (also underlined in the genealogy above), not necessarily, most of these psalms contain reference to the musical director, a superscription that might well have been added at the time of collation of the psalms into one book, and not final proof of authorship.

There is a very strong direction to another root altogether for the Ezrahites. It comes from a description of Solomon in 1 Ki.4.31.
' For he was wiser than all men; than Ethan the Ezrahite, and Heman, and Chalcol, and Darda, the sons of Mahol: and his fame was in all nations round about.'
Here is our man, or so it seems and here is the other Ezrahite too, his brother, although he is not distinctly titled.
Who was Mahol and who are these four sons, two of whose names are unique and Heman's unusual? Mahol's name means dance and well he might for joy for having such illustrious progeny. But his real name of course is taken from Heman's title, the Ezrahite, Zerah. Which Zerah could this be?

There is only one possible answer to that question.
'The sons of Zerah; Zimri, and Ethan, and Heman, and Calcol, and Dara: five of them in all.' 1 Chr.2.6.
This Zerah is the son of Judah by Tamar, itself a most mysterious & murky affair.
The names match almost exactly, and allowing for minor variant spellings (perhaps a scribal error with Darda) and the omission of the firstborn, for lack of the same excellence, it is exact match, not only by name but also by order.

Again it may be argued that these were far from contemporaries of Solomon, living around 6 centuries earlier, in captivity in Egypt. But is Solomon just to be compared with his own generation? Was God's gift only to be considered in his own time?
The verse before claims Solomon 'excelled the wisdom of all the children of the east country, and all the wisdom of Egypt.'
Is contemporary Egypt and the East intended, or all Egyptian and Eastern sages of all time until that point?
No, these four men excelled the wisdom of Egypt, just as their succeeding Israelite brother, Moses, rejected and saw through it.
Zerach's sons
It is parochial to claim the former, and unworthily restricts God's grace and the insight of Israel's prophets to a small silo.
Judah's sons

Ethan the Ezrahite authored Psalm 89 and Heman his brother the Ezrahite authored Psalm 88.
Are these the ancient sons of Zerah or the contemporary singers and arrangers of worship?

If Ethan had written Psalm 89 in Egypt during the captivity, generations before Moses, he not only predicted the name of Israel's king, but the character of the Messiah, the Beloved, just as a prophet forenamed Josiah (1 King 13.2) 450 years before, and Isaiah forenamed Cyrus (Isa.45.1) c.150 years before. He foresaw the collapse of Egyptian might, the future corruption of the Kingdom (which could easily be predicated on the idolatry into which Israel was already slipping in Egypt) and God's faithful promise of redemption through His Firstborn Son.

On balance, however we must favour the evidence weighing with the majority opinion. The citation of 2 Sam.7.14 could just be prophetic prediction, but it seems more likely to be contemporary allusion. Most decisive is the fact that if Ethan had made such detailed predictions of David's name, his prevailing over the nations of the Earth, the chastisement of his erring offspring and the astonishing covenant made between him and God, by the wisest man of the ages before Solomon, why had David not heard of it till Nathan surprised him, as God Himself has surprised Nathan (2 Sam.7)?

There is a curious and deep resonance between Ethan and Heman of Levi and Ethan and Heman of Zerah, perhaps Ezrahite was a contemporary epithet, a cousins' nickname which recalled illustrious forebears and namesakes. Or perhaps the true Ezrahites had indeed written prophetic odes, which provided the kernel and material for the later brethren to spin out into fuller more explicit lyrics of their own, all under direct inspiration, all God's own Mind and Word. For now the best solution remains a mystery. But what marvellous treasures they have left us!

*Incidentally the considerable variation in the number of generations proves the weakness of the argument that Luke's genealogy and Matthew's could not synchronise over a longer period on this basis.
**He like many Hebrews, including those in the NT, seems to have a second name and is also called Jeduthun. 1 Chr.16.38+, 1 Chr.25.1-6, compare with 1 Chr.15.17.19. He seems to have been active in producing new means of instrumentating music, Ps.39.1, 62.1, 77.1, where his name is used perhaps for a melody).