I agree with this. It is seems odd that the vet said fluoxetine wouldn't think it would be worth trying it considering you're thinking about re-homing. Even if it doesn't work for all dogs it does for some.
My friend's dog has similar issues about guarding, she's had the same problems with having workmen to the house. It escalated into the dog biting - it really is the hardest most complicated dog I've ever known. Several failed trainers and behaviourists.
This dog is also fine when alone, the behaviour is only an issue when other people are there. The drugs really helped it to be a happier less anxious dog in general. It was like his anxiety was so high it couldn't see past it for the normal behavioural stuff to work.
She got fluoxetine from the vet, it transformed the dog to the point she could work with a behaviourist. He's still not and never will be an easy dog, but he's now manageable for her. She can have people round to the house etc. They ran out of drugs once and noticed a huge difference in the dog. It is the drugs which help reduce the anxiety so they become trainable.
Could you try a different vet ?
My dog had terrible separation anxiety as a puppy, he would bark and bark and bark. I was completely housebound with him. I got a small cozy crate (first one I had was too big and scary), filled it with cushy things and chucked a sheet over. Then I made it somewhere he wasn't allowed in for a while - put food and toys inside but closed him outside so he was desperate to go in, left it like that for a week. One day I left the door open and totally ignored him in there. After that I'd just leave food inside and walk off. He started just hanging out in there hoping for good things to appear - so then I trained him with the door closed like you would sleep train a baby - 10 seconds and extend from there, never retun when barking, wait for even the slightest break before coming back in. He didn't mind being inside the crate with the door closed, but he didn't like me leaving the room, he was much better inside the crate though so I knew it was heading in the right direction. Once he was up to 20 minutes alone he was basically fine from that point onwards.
But my dog just barked and chewed things, he was terrified of being alone and needed a safe space and he adores all people, there was no growling etc. Your dog sounds more complicated in-general than my dog, but I don't think it gets much worse than my friends dog who had the drugs.
Sorry if this isn't the kind of information you're looking for and have already made the decision to re-home. Just thought I'd share in case any of it was useful. I don't think anyone would blame you for rehoming given the impact it is having on your family. It sounds really tough.