We have a giant yew with the same problem, we have decided just to hack it up and burn it. Replace with younger yew and keep it trimmed. I you have lots of thick old branches inside your boxwood it is probably not salvageable either, unless someone else here has more experience. Maybe the easiest to please your landlord is to yank it and put in a younger boxwood.
I think I’ll take one as an experiment and aggressively trim it back and see what happens.
My landlord is pretty easy going and if it dies he’ll probably tell me to 86 the rest of them.
Good luck with your yews and thanks for the reply.