פּירוש אויף דברי הימים א 25:3

and Mattithiah - six But you will find only five. [The answer is that] his wife was pregnant with Shimei, and he saw through the holy spirit that he too was destined to be the chief of a watch; therefore he says “six.” And that is what is stated further: (verse 17): “The tenth: Shimei.” This is what the liturgical poet set down (in the Kedushah of Yozer of Parashath Shekalim): “Inscribed from the womb to be counted in the watch of the Sanctuary.”

beside their father Jeduthun עַל יְדֵי, similar to (Neh. 3:8): “And beside him (עַל יָדוֹ)... repaired.”

who prophesied with [songs of] thanksgiving and praise For on the harp they would play songs of “Give thanks (הוֹדוּ)” and songs of “Hallelujah (הַלְלוּיָהּ),” and he would prophesy.