@jeffdnavarro asked "Or is there a point at which more dependents doesn't mean more credit? I am debating on whether or not I should let my ex-spouse to claim more dependents since the income is much higher".
Yes, there is such a point and you have reached it. You should also be aware that there is a special rule in the case of divorced & separated (including never married) parents. When the non-custodial parent is claiming the child as a dependent/exemption/child tax credit; the custodial parent is still allowed to claim the same child for Earned Income Credit, Head of Household filing status, and day care credit*.
At $15K income, you only need to claim one child for full benefits (including the child tax credit). Let the ex claim the others for the child tax credit, while you still get to claim them for the EIC.
For the 2020 tax year, he will even get the child portion of the stimulus/rebate credit, even though you already received it in 2020. However, if you did not get the full child stimulus ($1100 for kids under 17), in 2020/early2021, then you will have to claim them, as dependents, to get it on your 2020 return (or "make a deal" with the ex).
*This "splitting of the child" is not available to parents who lived together at any time during the last 6 months of the year; then only one of you can claim the child for any tax reasons. The tax benefits may not be split in any other manner.
Note in particular that the non-custodial parent can never claim the Earned Income Credit, Head of Household filing status or the day care credit, based on that child, even when the custodial parent has released the dependency to him.
