I find it very hard to determine the size of a button by looking at it. Sometimes when separating chicks from their parents at 6 weeks, I'm having serious issues telling the girls from their mothers - but the moment I hold the bird in my hand, I realize the mistake. The adults have a lot more meat on their bones. So I wouldn't even attempt to determine their nutritional status visually - catch them and weigh them or simply determine whether the bird in your hand feels like a bag of bones or has meat on its body.
With regards to getting 3 eggs a day from 2 hens, it's not entirely impossible. They can lay as much as an egg every 18 hours. But I'd definitely look further into the sexes, because if you really have 2 males and 2 females, you are very likely going to need a second cage eventually - more than one male in a cage that has females almost always results in some degree of pecking, chasing, stress or fighting.
Seeing as all your birds are gray, they are not all that easy to sex - but when you pick them up to determine whether they are underweight, you can turn them over and have a look at the feathers around the vent. The males will have a slight pink shade to the gray feathers which the females won't. Just beware that if any of them are all white on their underside, they are tuxedos and then you can't be sure the absence of pink means they are girls.
Don't make the mistake of thinking a white area at the chin means they are boys - they need to have the full array of black (or gray) and white markings, like the boy in Hybrids' pics, to be boys for sure.
They don't look thin to me, but I'd cut back on the finch seed (looks like that's the only thing in their dish on your pic?) and only give that as a treat, scattered around in their bedding to activate them. Depending on the protein content of the gamebird feed, though - I think
Manna pro might be one of the high protein ones? You want to end out somewhere around 20-24 % protein for buttons.
I'd also add some fake plants to the enclosure to give them places to hide.
