It's clear you are being deliberately obstructive to the kids having a relationship with their father due to your feelings about him from the fact that you haven't even considered asking the kids before asking mumsnet to try and get approval for your actions and from your replies when anyone disagrees with you.
The court agreement from 8 years ago was made as a minimum requirement for the care of young children based on circumstances at the time and in no way prevents the other parent from seeing them more when you aren't available to care for them, especially now they are older.
If your availability has changed since the original court intervention, as your ability to care for them for the periods in question is now different a court would very much be in support changing this agreement if he takes it that far, so you really need to consider your actions here carefully.
My sister acted the same way so I have seen this type of scenario in person as a third party and its not good at all, you need to put your children first and get over yourself, you are an adult, act like one.
It really is horrific when you see one parent actively preventing their kids having a better relationship with the other because of tensions between the two when they have proven for years that that it is a safe and caring environment for the children. You are actively blocking your kids from seeing one of their parents more without even asking their opinions because you don't like him at their expense.
I wouldn't be surprised at all if you bad mouth him to them or in front of them even 8 years later to try and influence their opinion of him to match yours.