BTW- the resource guarding might just be he has to settle in. I am sure he is a little shell shocked. I would be careful though- his size is enough to really watch him.
After he settles in, you can work on this resource guarding. When I use to put an adult in the house with other adults, everyoneeeeeeeeeee wore a lure coursing muzzle. That way no one could bite, and I could safely correct the behavior without getting bite. Also - is he neutered yet? If not, that might help alot.