I have a 5 week old Shih Tzu male puppy who is unstable on his feet. his two littermates are already very confident but he just wobbles about.
Hi
I would recommend taking this puppy to your vet for an evaluation.
As the other two puppies are not exhibiting the same issues, there is likely a problem.
Sometimes this can be caused by a neurological problem, or a hereditary health issue. It's impossible for me to tell, and you need a professional to figure out what is causing him to be so unsteady on his feet.
I'd suggest taking him for a check up as soon as you can, that way he can be diagnosed quickly and any treatment (if necessary) can be started.
Best of luck.