He will have to file a tax return since his self-employment income is $400 or more. He will need to complete a Schedule C for the self-employment income and expenses. If his Net income for the self-employment is less than $4,150 then you would be able to claim him as a dependent if he also lived in your home for the entire year of 2018.
But he must file a 2018 tax return for the self-employment income.
