The two dud injectors might be redeemable. Remove them and try soaking the spray tips (pintles) in carb cleaner or fuel system cleaner for a while (even overnight if you can manage it) then give the tiny pin on the end a couple of pushes inwards with a fingernail. It should move just a few thousandths of an inch with a definite but tiny "click". If they don't after a few tries, then they're probably dead. If they seem ok, re-fit them to the fuel rail and see if they work. If they don't, you've lost nothing by trying.
Of the ones I've tried this on, about half were saved.