Lots of dogs react much more on lead because they can't get away so they make a big show to tell the other dogs to bog off, it sounds like he is a bit fearful and that's why he is reacting. With lots of socialisation and dealing with this in the right way it can usually be greatly improved.
You can use toys for reward based training, it doesn't have to be food. Just be careful about which ones and in which situations if he can be guardy with them. Re the food, you can use his daily rations for training, often with dogs that aren't very food motivated, if they feel a bit full then they aren't bothered. But if they are working for their dinner they can be different
Also try some really high value treats like, hot dog sausage, roast chicken, especially if it's just been warmed up, lots of dogs love cheese, regular cheese or primula in the tube, easy to cary around aswell. Some dogs love dried salmon.
As he's got a couple of fairly big probs I really would go to a behaviourist, either get a recommendation from your vet or if you say which area you are in someone on here may be able to advise of one in your area.
In the mean time just manage the situation as best you can by avoiding putting him in those situations, make sure all toys are cleared away so he doesn't get the chance to guard them if they are left lying around.
If someone else comes into the room and he is sat next to you, then either ask him to go to his bed or you move away from him or pop him in another room if necessary.