Still not enough details, and what's the question?  They alternate both younger children? So he claims two for 2024, and she claims two for 2025?  I'm sure there was a good reason for both just claiming one every year.  The divorce decree is highly relevant if one of them doesn't follow it and the other wants to enforce it in state court, especially if there is no custodial parent (equal nights because of summer camp or grandparent visits).  

Yes, I would enter all three of them and use Q for those not claimed.  That way it's easier to track the SSN and DoB.  IRS is not going to get involved unless a kid is claimed by both.  Potential problem is when the older kid leaves home and both parents want to claim HoH.  Best solution is for one of them to remarry.