Joram had written one letter. This was the next. Alternate translation: "again wrote a letter to them" or "wrote another letter to them" (See: [[rc://en/ta/man/translate/translate-ordinal]])
To "be on someone's side" means to be loyal to them and supportive of them. Alternate translation: "loyal to me" (See: [[rc://en/ta/man/translate/figs-idiom]])
It is implied that they are to bring the heads of the Ahab's descendant and present them to Jehu. Alternate translation: "you must take the heads ... and bring them to me" (See: [[rc://en/ta/man/translate/figs-explicit]])
This refers to killing them and removing their heads. Alternate translation: "kill your master's descendants and cut off their heads" (See: [[rc://en/ta/man/translate/figs-euphemism]])
This means that they were supervising them and teaching them. Alternate translation: "who were raising them" or "who were supervising them" (See: [[rc://en/ta/man/translate/figs-idiom]])