Also a difficult question for me to answer, but sounds like you are doing fairly well at the moment, rule of thumb is feed every 4 hours except for real tinies where they can't keep their blood sugars up, this really just includes poms, chihuahua's, yorkie's & the like!
If your pups are feeding well & eating what you put down within minutes, then up it a bit the next meal & see how they go, I doubt you're underfeeding
& if you were overfeeding you would have puppies with loose poo's.
Hope that helps

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