It depends on other things if you can claim him. He had to only make under 4,300 to claim him.
How old is he?
Was he a full time student?
It doesn't matter who files first. If he qualifies as your dependent he has to check the box that says he can be claimed on someone else's return.
Did he get a W2 or 1099Misc or 1099NEC?
You don't have to file if you only have W2 income under 12,400 but you can file to get back any withholding taken out in boxes 2 or 17. But you don't get boxes 4 or 6 back. If you got a 1099Misc or 1099NEC you have to file it as self employment income no matter how small the amount.
To file a separate return as a dependent you need to set up a new account separate from your parents. Online is only good for one return per account. You can use the same email address for 5 accounts. You can probably use the Free Edition or the Free File website
Https://ttlc.intuit.com/questions/1894512-how-do-i-start-another-return-in-turbotax-online
Be sure on your return you check the box that says you can be claimed on someone else’s return. If your only income is W2 and under 12,400 you do not have to file a return except to get back any withholding taken out.
Filing requirements for a dependent
https://ttlc.intuit.com/community/children-dependents/help/do-i-need-to-file-my-own-taxes-if-i-m-a-d...
