There is nothing for you to update since you will be claiming the children as dependents on the 2021 tax return that you will file next year in 2022.
The Advance Child Tax Credit being distributed by the IRS in 2021 would be only available to the party claiming the children as dependents on a 2020 tax return. If he receives those advance payments and does not claim the children as dependents on the 2021 tax return he will have to pay back the advance payments received.
