The sons of Jeduthun - six - That is, six with their father, otherwise, there are but five. Hence it is said, they were under the hands of their father Jeduthun, who prophesied with a harp, etc.
3. Six. Only 5 names are here listed. The list in vs. 9-31 suggests that the missing name is Shimei of v. 17 (see on v. 9). The LXX includes the name Shimei, placing it 4th in the list.
Who prophesied. See on v. 1.