The word "blood" is a metonym for murder. And, the idiom "blood return on the head of" means the person should be considered guilty for murder. Alternate translation: "I want Yahweh to hold Joab and his descendants guilty" (See: [[rc://en/ta/man/jit/figs-metonymy]] and [[rc://en/ta/man/jit/figs-idiom]])
The words "house" and "throne" are metonyms for the family and the kingdom. Alternate translation: "to David's descendants and to David's kingdom" (See: [[rc://en/ta/man/jit/figs-metonymy]])