It sounds very difficult.
My dog was similar and Prozac was helpful.
This will be controversial here but I also found that doing a lot of training with him helped create an atmosphere where he recognised I was in control.
His anxiety and snappiness escalated because I became fearful of him...and that is quite a natural thing if a dog has bitten, because of course you are fearful of it happening again. But dogs are very sensitive and tuned into how you act, and if you are nervous then they become nervous, and reactive dogs can get a pre-emptive strike I'm first.
So I started out on strict training for lots of different commands and rewards accordingly. I had to cultivate at environmental of calm assertive authority, this meant my dog knew the rules more, he gained confidence in knowing what was expected of him and his reactivity reduced.
You can do all the training in a very hands off way...and in fact this is very helpful during this stage if they are reactive over body touching. So you instruct the dog to get off the sofa, into the car etc rather than lifting them. I would always instruct my dog to come to me to have his lead put on as this showed his agreement to the process rather than me going up to him to put his head on.
Over time this works for more and more things, so you instruct the dog to fulfil a few commands and then come to you for grooming, and that meant body handling was possible again. It was absolutely key to create an attitude of compliance in my dog.
I'm sure I'll have accusations of using dominance thinking etc, but this was an entirely positive process, it had to be, my dog had zero tolerance for anything he didn't want to do to start off with.
He was very food motivated so that meant this was all very achievable.
But what all of this meant was that our relationship changed, his attitude towards me shifted and I was no longer someone he felt entitled to snap at, or uncomfortable around because he could sense my nervousness around him, which provoked his own.
The training was all done outside of high stress situations...so if he was highly aroused about something I would ignore altogether as any response could escalate. We did the hard graft at other times, and that reduced those stress responses in general.
He's now a dog who very happily shares the sofa or bed with me. That simply wouldn't have been possible before this process. If he had been on them first he would have growled at my approach. If he had jumped up on one when I was already there and I had attempted to stroke him, he wound have snapped at my hand. No issues now.
What I do still struggle with is feeling confident to leave him with others however, and that is a big limitation on our lives.