Advise needed on reducing fast off morphine.

My husband is reducing his morphine. His NSCLC' scan has just shown no cancer, though he still suffers pain from an operation his oncologist said he could reduce. He is reducing 10mg morning and evening every day. Does anybody know is he reducing to quickly? In the September he came out of hospital on 300mg morning and evening with fast acting 30mg and 20mg x4hourly if needed. Xmas he was down to no fast acting during the day and 170mg morning and evening. 29th January he had managed to bring it down to 110mg morning and evening and from then on he is bringing it down 10mg morning and evening. He is now on 50mg morning and evening. Please if anyone can tell me if this is alright or if it can harm him and whether he should stay a couple of days on the same amount. Does anyone also know how long Morphine stays in the body for? How does he come off the last 20mg/10mg? Any ideas appreciated, thanking you for reading the question Lo