Is there an issue with the kids sharing a bedroom? Meaning, is there harm because of this? Ideally, it would be good to seperate them by puberty, but it is what it is. You do what you can as effectively a single parent.
As for your draft:
Next week we will follow our visitation schedule. There is a custody agreement that we agreed, signed, and registered into the court. I am advised to abide the court visitation schedule by my lawyer and documenting everything. If you want to make changes, it needs to be done with a mediator or through lawyers.”
BIFF it and don't give him ammo. You don't need to explain yourself. There's a court order.
Though it's natural to fall into the emotional stuff, as this is triggering, imagine Spock: logic, no emotions.