The word "his" refers to Joab. "Blood" is a metonym for murder. And, the idiom "his blood on his own head" means the person should be considered guilty for murder. AT: "Joab has murdered people, and I want Yahweh to hold him guilty for what he has done" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-idiom]])
These words mean basically the same thing and emphasize that Abner and Amasa were much better men than Joab. (See: [[rc://en/ta/man/translate/figs-doublet]])
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. AT: "I want Yahweh to hold Joab and his descendants guilty" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-idiom]])
The words "house" and "throne" are metonyms for the family and the kingdom. AT: "to David's descendants and to David's kingdom" (See: [[rc://en/ta/man/translate/figs-metonymy]])