Alternating Multiple Dependants

In 2020, I claimed 2 of my kids and my ex claimed 1. In 2021, I will claim 1 and he will claim 2. I am currently being sent the child tax credit for 2 kids. My ex believes that I am stealing his money, because he will not get the full credit when he claims our 2 kids for 2021, because the IRS is sending me half. Is this true? Do I need to completely unenroll and receive nothing until tax time? Can I continue getting the money for both kids and just pay back for 1 child without it effecting my exe's tax returns.  The IRS stated there will be a way to adjust dependents "later this summer". Do you have any further information on this?