support? Not just for half of the year? From the instructions: "Who didn't provide over half of his or her own support for 2018".

I was advised by a tax professional that if we couldn't provide strong evidence of providing more than half of the child's financial support for the year, we would be in trouble if audited. And that this is a relatively common flag for audits, since they can see the child's AGI on their return. Luckily, our dependent just had a summer job at Lagoon, so her income was low enough that we could justify providing more than half of her support.

Since the OP stated both his son's have fairly good income, he would have to be able to show that what he provided (cost of housing, medical benefits, food, etc.) throughout the year was more than the son's personal income.