Here the word "he" refers to Paul. Cenchreae was a seaport that was part of the greater Corinth city area. (See: [[rc://en/ta/man/translate/translate-names]])
This continues Paul's missionary journey as Paul, Priscilla, and Aquila leave Corinth. This seems to indicate that Silas and Timothy remain since it says "he" here and not "we." The word "they" refers to Paul, Priscilla, and Aquila.
The word "brothers" refers to men and women believers. Alternate translation: "left the fellow believers" (See: [[rc://en/ta/man/translate/figs-gendernotations]])
This is a symbolic action that indicates the completion of a vow. This can be stated in active form. Alternate translation: "he had someone cut off the hair on his head" (See: [[rc://en/ta/man/translate/translate-symaction]] and [[rc://en/ta/man/translate/figs-activepassive]])