If a person qualifies to be claimed as a dependent by someone else, they must answer “yes“ to the question, “can someone else claim you as a dependent“ even if the other person agrees not to claim them. For 2020, if they answered no, that no one can claim them as a dependent, they would be eligible for the $1200 round 1 and $600 round 2 recovery rebate. However, this will probably be considered tax fraud although we don’t know how strongly the IRS will be able to enforce this. The IRS has three years to audit a tax return or six years in the case of deliberate fraud.
The round 3 payment is $1400 per person including all dependents, not just dependents age 16 and under. So the total amount of the round 3 payment will be the same no matter how they file their returns. If they answered no, that no one else can claim them as a dependent, then they would receive $1400 each. If they answer yes that someone can claim them as a dependent, and you do in fact claim them as dependents, then you would receive $1400 for each of them plus yourself. If you have not filed your tax return yet, then I believe the IRS will make the round 3 payments based on your 2019 tax return. Or the IRS may make catch-up payments when they receive your 2020 return. There will likely be an opportunity to claim a rebate at the end of 2021 for your dependents if you do not receive a payment during the year.
having your dependents file amended returns to change their answer from yes to no, that no one else can claim their them as a dependent, would not only possibly constitute tax fraud, but would confuse and delay things even more than they already are, because amended returns take 5 to 6 months to process.
