I want to send you love and support right now. You are living a nightmare and it sounds as if you've been doing so for some time. I'm in awe of the support and compassion you and your husband are giving your brother.
But I have to be blunt…I really think you should consider getting him into a strict in-patient program. This is too much for you and your husband to bear. Your brother is in the grips of a deadly addiction. I feel for him too. He is in hell now. And not just because he's tapering off benzos and thinks he needs more. If it were as simple as following a wise, proven taper, the Ashton Manual could provide you with practically everything you need to ensure a safe and gradual result.
But your brother's manipulating you by threatening to buy crack. You've had to sleep next to him so that he won't drink mouthwash or inset-repellent. You're suffering from insomnia now because you're waking up at night to make sure he's not harming himself with more substances. He's ordering more meds off the internet. You have no idea what he has and what he's taken…
This is more than 2 people can bear and it may not be in the best interests of your brother to continue to support him in this fashion. This is way more than managing his taper. And continuing this dynamic may eventually damage your relationship with your husband and with your brother.
I have so much respect for the support you've given him and the research you've done into his affliction. You are a straight-up wonderful, caring person. Many people would be immeasurably grateful to have family like you. But I think he may be better off in an environment where he can't manipulate the people who are responsible for managing his rehab.
You said he's been through a number of "luxury rehabs." It sounds like he may need to be in a place where the rules are strict and lots of physical work is part of the rehab. I have a friend who was as desperately addicted, albeit to heroin and crack, and he spent 2 years in a facility (Walden House) to learn to live clean and to work a normal job and get along in society.
I was surprised to do a search on Walden House and read some negative press and a hint that it might be a cult(?!). R. thought it saved his life. And he was a tough Italian Brooklyn boy (man) who, if any topic arose relating to spirituality, he'd let loose with all the Sopranos language that he grew up with. Yeah, that kind of family. R. was fucking intense. Your brother sounds very intense too. It's just that his intensity is channeled in a destructive direction right now.
I haven't offended by my comments. I've already said so, but I have so much respect for your compassion and dedication. I just hope that one day, if he can get the right treatment, you can enjoy a healthy relationship with your brother. I really wish you the best.
Positive vibes and love,
e.