My name is ***** ***** I have been a solicitor for more than 35 years.
This is to add to the above.
There are a number of issues here.
It is not reasonable for your ex to refuse to allow you to take the Children on holiday because "she is not ready"
Children are entitled to a close relationship with both parents and if you are able to care for the children then you should be able to take them away.
It is also entirely inappropriate for your six year old to be involved in any of the discussions regarding the time she spends with you - she is not old enough and these are adult matters.
having said that if you have not yet taken the children away for short holidays within the Uk then it is unlikely in the extreme that the Court will agree to your taking just the eldest away abroad skiing as a starting point.
You would be better seeking permission to take both the chidlren away in the Uk for short periods of time and then a full week or ten days in the UK with a trip abroad the following year.
The starting point is to try and discuss matters with your ex using Family mediation
Only if that fails is a Court Application the next step - and you should apply for a Child Arrangement Order
Please ask if you need further details