A typical Probate File should contain the will, a form detailing the deceased’s estate (as listed by the executors) and the oaths signed by the executors. NAS in Dublin appear to be charging for copies of each of those documents. It can cost quite a bit to get the lot but only you will know how much you need them.
Where there is one, the will is obviously the key document. The probate document can be useful (form B1 for the Inland Revenue), especially in intestacy cases (i.e. no will), as it can list property you wouldn’t otherwise know about. The oaths are generally the least useful as they only tell you how the executor was related to the deceased (if there was any relationship) and about surviving next of kin. However that information is also often on the B1 form.
I would just order the will and see if that tells you what you want to know.