Have a lead handy at all times. Clip on the lead and remove him from the room, re-enter, if he starts, remove him again and so on.
Sounds like fear barking to me.
Strange objects or funny looking people, often if people speak the dog relaxes oh it's only a person. A RR did that to my SS the other day at a show because he had a blanket over his head to stop the glare on his ninetendo screen. Once he spoke the dog relaxed.
While you can't really take him up to smell the drunks lying on the road I'll often take a dog up to the object that frightens them or go and touch it myself. Remember scent is stronger than sight for a dog.
As for the house have you tried throwing treats, when he goes off at people? it distracts the dog, he goes quiet while he locates the treat and is rewarded
Just throw off to the side of the dog.
I think you need to set up training for this type of thing, have someone come over two or three times thru out the day and practice it.
Can you move his bed to a more private corner of the lounge room. Is he protecting his bed or does he feel more safe there which is why he retreats to there and barks? I think you may find it's the latter?? Is this room further into the house??
Another thing to try, but with caution is to put him on a lead, he's in the middle and you and the other person are on the outside of him, after a few steps pass the lead to the other person and they keep walking while you fade away, they pass him treats etc. We would do this at the kennels for fear aggressive dogs. Again it's a practice thing