I've recently finished writing an article on nutrition and another one on dental health.
In the research that I did, I found it amazing how many carbohydrates are in cat and dog food. In their natural state, cats and dogs do not eat many carbs at all, relying on the energy they need from protein (sourced from other meat, and to a lesser degree plant protein), and also from fats (which are naturally present in meats). Also in their natural state, cats and dogs would often not have a pre-prepared meal waiting for them and would need to fast due to the lack of food available.

Dog's teeth are naturally ultra-white in colour (more so than the whitest white that a Hollywood dentist could achieve). They should not have smelly breath at all - smelly breath indicates bad dental hygiene.

And absolutely, puppies should always be on a food specially formulated for puppies. Perhaps you could say to your auntie (or get your mum to) that if a puppy isn't fed on puppy food, it could be detrimental to their growth and they will not develop the way that they should.

So with this in mind, I would recommend finding a good quality pet food that is meat-protein based, feed frozen bones to keep their teeth and gums healthy, and perhaps have them skip a meal once or twice a week. I know this sounds harsh, but when you consider that up to 1/3 of pets these days are overweight, this may not be such a bad feeding regime...? JMO