I feel a bit feeble here because having gone through very similar things with Lenny over the last 18 months, I feel I should be able to help but am not sure whether I can.
Firstly, I agree that getting a behaviourist in would be a good idea if you can find a good one. I have heard a few stories about people not being fortunate and therefore decided not to.
Secondly, time helps. Change may be gradual but you will see it if you stick to sensible, consistent treatment. It's great to see your dog's behaviour improve.
Thirdly, Mine! is worth reading but won't give you any easy answers. How you use it depends on your approach to training.
Fourthly, time is important in another way. You need to give your dog a bit of time to accept that he's going to do something. As an example, as your daughter has seen, it's not a good idea to stick your hand in quickly to get a dog with this type of problem to move. I have had a number of bites to confirm that. If instead you turn to face the dog give a command to get down and then just wait for him to respond, he is likely to realise that it's probably a good idea to stand down from the worktop. In a similar way I had a number of stand-offs with Lenny, who had problems with food aggression as well as possessiveness with toys etc. In particular, on walks he would occasionally start eating poo and growl if I approached. If I tried to put him on a lead quickly I would get either a snap or a bite. If I waited, and stood next to him, his mood would eventually change and I could put him on the lead and take him away. Often he would show his displeasure by attacking my walking boots but I just stayed still and silent and let the moment pass. Now, I can tell him to leave the poo and walk on, and I feel confident that I can reach out for his collar to put him on the lead without risking a bite. I will always keep a check on his mood and give him more time if I need to.
I expect I am going to be criticised by behaviourists who will say I have got everything wrong, but I think you need to gently challenge the behaviour without being aggressive. So in the case of Murphy occupying the doorway, move a bit closer and let him growl for a bit without feeling too threatened then move away without trying to take anything off him. Maybe give him a treat, throw it if necessary, and then move away to show that it's not a bad thing to let you come nearer. When you feel confident enough, and maybe there's a bit more space than usual, walk past him when he's stolen something without paying any attention to him or the stolen article.
It's hard work and you will get relapses but I think the reward you get from improving the behaviour of dogs like this is brilliant.
I wish you all the very best as you help him overcome his problems and I am sure that you will have a fantastic dog in the future.
