I am just thrilled to hear all the good news and see this boy in his new home. That doggy door will be a boon when it comes to housebreaking as will his being able to observe his new siblings. It is so sweet to hear how he loves being petted and playing with toys.

From everything you have said, I just have a feeling that things will work out just fine. When your other two give him a growl, they are just letting him know to back off a bit and obviously he is understanding their communication. It doesn't seem as if he will challenge them and with their being older and well trained, it doesn't seem if they would want to start any argument.

Does he seem to have any problems with separation anxiety? Have you left the house for a few minutes or longer to see how he will react?