Charles Ellicott Commentary 2 Chronicles 5:12

"also the Levites who were the singers, all of them, even Asaph, Heman, Jeduthun, and their sons and their brethren, arrayed in fine linen, with cymbals and psalteries and harps, stood at the east end of the altar, and with them a hundred and twenty priests sounding with trumpets;)" — 2 Chronicles 5:12 (ASV)

All of them of Asaph ... brethren. —Hebrew: to all of them, to Asaph, to Heman, etc., and to their sons, and to their brethren. This use of the particle le (to, for) is characteristic of the chronicler, whose style in these verses stands in marked contrast with the former part of the chapter. Regarding the Levitical guilds of musicians, compare 1 Chronicles 25:1–7; 1 Chronicles 15:16 and following.

Arrayed in white linen. — 1 Chronicles 15:27.

Having cymbals and psalteries and harps. — With cymbals and nebels and kinnors (harps and lutes, or guitars). (See 1 Chronicles 15:28.)

Stood at the east end of the altar. — Were standing east of the altar.

And with them ... trumpets. — And with them priests, to a hundred and twenty, were trumpeting with trumpets. (See 1 Chronicles 15:24.)

A hundred and twenty. —Thus five to each of the twenty-four classes of the priests.

The parenthesis should be removed.