My son (died in May) made over the allotted amount to be claimed a dependent on our taxes. Is there a way to add him to our taxes or do I need to file his separately?

A child's income earned from working is never put on a parent's tax return, the child must file a return in their own name.

Sometimes if the child's only income is interest and dividends, and the child is under age 24, the income can be reported on a parent's return.

If their income is less than $12,950, a tax return is not required unless they had more than $1100 of unearned income (investments, prizes), or their income was from self-employment.  If a return is required, you will need to make a separate account.  There is a procedure to follow when filing a return for a deceased person.

https://turbotax.intuit.com/tax-tips/family/death-in-the-family/L5albFXM4