This little guy is so fearful of everything and everyone! If he was abused, as it sounds he was, he has no reason to trust; not yet at least. I have a "PawPal" named Black Jack. He was rescued from a puppymill. He is a Chihuahua too. Like your little guy, it is taking him a long time, a lot of loving and tons of patience to help him regain trust in humans. It is a journey made up of lots of baby steps. On top of everything, your guy was also recently traumatized by his injury. It will probably take a lot of time and patience on your part. Isolating him in an area where it is quiet and he does not feel threatened is a good first step. Do you have an extra bathroom, guest room?? Maybe a small crate, with the door left open, would give him some sense of security. He should learn to interact and trust you first. Introductions to other pets and family members should be taken slowly. Maybe have another family members be with you, each holding one dog, so the two can "meet," smell, learn to know each other safely. I hope you can give this little guy a bit more time to help him heal, emotionally and physically. Of course, your first concern must be for Tango. If you feel it is becoming too much of an undertaking, perhaps you can locate a rescue group that can find a loving foster home for him?? Many fosterers deal exclusively with abused dogs with special needs. I'll be thinking of you. And thank you SO much for being so kind and caring. Please let us know how it goes.