5-7 are definitely carp. The barbels, the more slender body shape and on 5 and 7, the reflective scales along the top of it's body indicate so. These fish are better suited outside in a pond, and they will undoubtedly outgrow your tank. But, if you can put up with them uprooting plants and digging around in the dirt, there's no reason why they can't stay where they are for now, althought they feed more vociferously than the fancy ones, so they may just be getting a lions share of the food
Thanks. I'm planning on leaving 2 of them in the 30G tank until they hit 6" (they are now about 2" each) and then donating them to a neighbor's outdoor pond.