Anyone who falls within the income guidelines and is paying $4,000 or more in educational expenses per year will be eligible for the full $2,500. Each of your students is eligible for their own credit.
The loophole you mentioned is this. If the scholarship is greater than qualified expenses (tuition, books and any required fees) you have discovered that you can’t take the credit because all of the expenses have been covered by the tax free scholarship. BUT if you don’t use the scholarship to pay for those education expenses, you are then free to report that you paid for them yourself and so can take the credit. The scholarship amount will be income to the student but lacking other income they probably will not have to file anyway. So “tell” the program that you didn’t use $4,000 of scholarship for education expenses. By all means you should claim your students as dependents. You can’t get the credit otherwise.