[Marilize]

Sorry to tell you this, but your yelling is only adding to the situation. I recently spoke to an animal behaviorist and she says that the best way to handle these situations is to quietly walk away when you see that there is building tension between them. They interpret your yelling as just another dog adding to the tension. So, just take a deep breath and walk away. The babies will follow you and the tension will be gone.
Also, they have to sort out the dominance issue for themselves. If the older one is growling and showing teeth when the other dog is being irritating, the other dog is merely teaching the dog what appropriate behavior is.
Don't interfere with the dominance/submission issue. They have to sort it out for themselves. By asserting your idea of who should be in charge, you are only prolonging the inevitable and making the process very stressful. The more dominant dog will continue to try to be dominant and will eventually be, so just leave them to sort it out for themselves.
Of course, use your judgement with the dogs, but don't freak out or yell at them (I know it is hard). Let them sort it out.

Good luck.