8 weeks should be fine then, they just looked younger to me! Weird things happen when you mix breeds, sometimes they look so much more like one parent than the other. My dog has medium length hair (like golden retriever length) with long hair on the tail and ear fringe but both his parents were completely smooth coated! I wouldn't have guessed shih-tzu since their muzzles seem to be a normal length and they don't appear fuzzy (hard to tell in photos sometimes), but Chihuahua seems possible, or a small terrier like a rat terrier. But once they grow up a bit it may be easier to tell.
Good luck with the cuties! I can't imagine trying to do two at once!