They sound pretty normal :)
Some thoughts: your desire to instill positive eating habits may be backfiring. Because you are rationing "treats" by giving out "tiny crumbs", its possible you are making these items even MORE attractive that they would be otherwise. This can lead to eating disorders later when too much emphasis is placed on "right" or "wrong" foods. Consider giving them a little more free reign with foods. They will probably go nuts at first, but after time (and some patience by you) they should level out where those "treats" aren't such a big deal anymore and eating healthy is part of their balanced meal.
It may also be that they are merely going through a growth spurt! My little ones go through periods of caring less whether they eat and then suprise me by having periods of varocious appetites!!! Sometimes I don't know where they put all that food. After every weight gain and pudgey period, they shoot up and get thinner again only to go onto the same cycle down the road. I would not worry if they seem a little pudgey...that means they are growing like all other children :)
On a longshot (and I really don't believe this applies), you might consider supplementing their diet with lots of crunchy veggies on the off chance that their nerves are seeking additional input to develop a healthy nervous system. Some children have sensory delays while developing (which are actually fairly common). Oral motor delays can manifest in a need to overstuff the mouth or constantly searching for stimulation. By providing crunchy items and differing textures, you can help stimulate the nervous system to make those connections necessary for healthy development. AGAIN, I seriously doubt this applies but it is food for thought...and if it were the case, it would be a temporary situation easily remedied.
Best of luck to you and your twins!