Thank you for your question
My name is Clare
I shall do my best to help you but I need some further information first
How old are the chidlren now?
The problem that you face is one of timing.
Yes you can apply for it to cover Tertiary education (University) - provided you apply before the child is 18.
That is done using a Form A and paying the feeof £245
However at that point you may provoke your ex into involving the CMS - which can be done 12 months after the Order is made - and their assessment will override the Court Order
Accordingly leaving it later may be wise - provided you apply before the eldest turns 18, as once the Court Order no longer applies - because your child has left secondary education - the Order cannot be changed by the CMS so far as the eldest child is concerned.
I hope that this is of assistance - please ask if you need further details
How much time does he actually spend in the UK?
During the court process did he use the Irish address as his home address
You shoudl certainly wait until about six months before your son turns 18
The CMS is the Child Maintenance Service
Yes you can still apply here in the UK as the Order is in existence.
You can also apply for an upward variation at any time