You will need to file a separate return for him.
Yes, you can still claim him as a dependent as long as he was under 24 at the end of the year and did not provide more than half of his own support.
He probably does not qualify for the Earned Income Tax Credit. To qualify for the EITC you cannot be claimed as a dependent on someone else's and if you do not have a dependent of your own you must be at least 25 years old.