I had some jealousy issue's initially when i first brought home one of the puppies with my almost 2 year old Yorkie. She would growl at little Cinnamon and constantly push over as if to show her SHE was the alpha dog. I tried to spend extra time using distraction with them and she seems to be past it now. Anytime I would bring Cinnamon out, I would immediately get a couple toys to start distracting both of them by teasing them to play with the toys. they would ultimately end up playing tug awar with each other.
Your 5 year old yorkie is just worried that he might lose you since he has had all of your attention for so long.
Eventually he will probably come to terms and enjoy the new addition once he realizes he can still be the (YOUR) alpha dog
