Who paid for over half of the son's support?

Depending on the circumstances, the parents MIGHT be able to claim him as a Qualifying Child.

You'll need to determine if he meets the tax definition of "permanently and totally disabled" (see first link).

And $17,000 could be under the "substantial gainful activity" .

https://www.irs.gov/publications/p501#en_US_2024_publink1000220897

https://www.ssa.gov/oact/cola/sga.html