The chatterer's repeat instructions to the dog: "Rover, rover, Rover, ROVER! Ok, now sit. Sit. SIT! Siiiiiit. Good dog, good boy."
The conversators have an ongoing conversation with their dog: "Now are you going to be a good dog and Sit for me? Good dogs sit, can't you sit? What? Do you hear something? It's nothing, just go ahead and sit down for me."
Neither group gets their point across to the dogs. There's just too much talking going on.
Dogs aren't programmed with verbal skills. Sure, they can figure out that when you say "biscuit," something good always follows. But that doesn't mean they understand our language.
To better communicate with your dog, try talking less. Silence is golden, as the saying goes.
Use one-word cues to get behavior. Instead of "lay down," use either "lay" or "down." How confused is your dog when you say "lay down" and "sit down" -- both contain the word down (which may also have a meaning to your dog).
So, you've said the word "sit," and your dog looks at you - now what? Wait him out. Don't repeat the word. Look off to the side, at the floor. If the dog doesn't sit within a few seconds, simply walk away. No admonishment, no lecture, nothing. Just leave. Come back in a few minutes and try again.
If he does comply, have a little party and give him a tasty tidbit.
After only a few experiences with this new, less talkative you, your dog will get the idea that if he doesn't do what you ask, he doesn't earn any reinforcement. It's up to him, not up to you, to comply. Simple as that. (Note: He doesn't get in trouble for not complying - he simply misses out on this chance to earn a reinforcer.) Another great side benefit: your words become golden to your dog - they could lead to an opportunity for him to earn a reinforcer. He doesn't want to miss a word you say, and therefore is super-attentive.