Why does his breath smell like rotting pumpkins?

Vet says theres no broken or injured teeth.

She suggested greenies, and a couple other dental treats.

There's no poop he can access to eat as we don't have cats anymore.

He takes 2-3 big healthy ones a day outside. So I don't think he's hiding an accident. He's outside every 3 hours. Even if he doesn't go.

I feed them Whole Hearted beef, for small dogs. (Anyone else notice kibble size is normally geared towards bigger dogs, I need Itty bitty pieces, they're tiny dogs)

Could it maybe be the food? Could it be the treats? I use blue wilderness soft treats, they won't eat the biscuits.

They are my first dogs, honestly idk if it's normal or not. (Only one with the breath of death, the big guys isn't too bad, but still smelly.) Vet says some smell is normal, but she thinks he's eating poop.

I'm like 80% certain he's not, he's really never out of my sight. He's a lapdog, and cries if he's not up my butt.

I have been looking at one of those finger brushes for their teeth, but idk how they'll react.

Any ideas?