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

OK, thank you! It sounds like I don't even have to worry about it since he made under the $12K (and none of it was unearned income).

So sorry for your loss😪. It's true you don't have to file for him, but if he had taxes withheld from his income, it would be all refundable. His Personal Representative can complete and sign his tax return, if you want to get the taxes withheld refunded.