Sometimes a hen will target chicks that are a different color. Or, being the last 2 to hatch, she may sense that they may have a hard time keeping up with the rest. You can leave them and hope for the best, or remove them and raise them artificially. If you do the latter, you are apt to have a difficult time integrating them, as she will view them as a threat to her "accepted" clutch. Depends on your flock dynamics, amount of available space, and your flock goals. You might even consider finding someone who would welcome a couple of orphan chicks and give them away.