Whilst not stated, I take it the deceased died intestate.
I believe the primary grant should normally be obtained in the deceased’s “home” jurisdiction. If domiciled within the UK, the question will be whether his domicile of origin of Scotland was revived, so that a Scottish confirmation would be the primary “grant”.
If he had established a domicile of choice at the time of his death, then I would expect the primary “grant” to be obtained in that jurisdiction.
Having said the above, I recall the Netherlands my look to residence rather than domicile or nationality, so that there could be a competition between there and Scotland as to which is the primary jurisdiction, and which Succession Law applies.
If the deceased died domiciled within the UK, any grant issued within the UK would be limited to UK assets in any event. If he was domicile outside of the UK, then any UK grant would only give title to assets within that particular jurisdiction (England & Wales, Scotland or Northern Ireland).
So far as the UK is concerned, the children would be entitled to apply for representation. At this time, only the older child, or their attorney/factor would be able to apply.