The plural for of "tú eres" is "ustedes son" (unless you are using "vosotros" from Spain, in which case the answer would be ¡Vosotros estáis estudiantes atléticos!)
Then, you just need to add an "s" to the end of the adjective and noun "estudiante atlético" to make them "estudiantes atléticos."
I hope that was clear. Let me know if you have any questions about my answer!
