I think you've got two little doggies wrapped around your paw
They are probably going to do this pickyness thing with every food you try because they've learned the minute they stop eating, they get a new food. Believe me, I went thru it with Jackson. Eventually, I just decided he's going to eat... and it's been going good so far. We're still doing Acana and have been for over a year now, with a few different foods in between, but mainly Acana. He tired of it for a while, so I switched to Orijen, and once I was back to Acana, he loved it again. So that's why I switch flavors and/or brands after every bag to keep him interested.
Granted, I'm still a dog nutrition nerd (LOL) so am always looking for new things to try that he's happy with. Of course it's nice to see them enjoying their food. I've always mixed with wet for this reason. I got sick of seeing dry food sitting in a bowl day after day.
But small kibbles I know of - I consider NV pretty small. Fromm is teeny tiny. Natural Balance has a small bites.