I am informed by Revenue that it is not possible to be definitive about the inheritance tax position in this case given the absence of specific information.
For inheritance tax purposes, the relationship between the person who provides the inheritance (i.e. the disponer) and the person who receives the inheritance (i.e. the beneficiary) determines the life-time tax-free threshold - known as the Group threshold, below which inheritance tax does not arise. It seems that the question may relate to a potential future inheritance passing between siblings, in which case, the Group B threshold (currently €32,500) which applies, inter alia, where the beneficiary is a brother or sister of the disponer would be relevant.
Any prior gift or inheritance received by a beneficiary since 5 December 1991 from within the same Group threshold is aggregated for the purposes of determining whether any tax is payable on a benefit. Where a person receives inheritances that are in excess of his or her relevant tax-free threshold, inheritance tax at a rate of 33% applies on the excess over the tax-free threshold.
While there are no specific reliefs provided for siblings living together, they may bequeath assets to each other free from inheritance tax provided the value of the assets does not exceed the relevant tax-free Group thresholds when previous gifts and bequests to the individual are considered.
In addition, siblings can avail of the ‘dwelling house exemption’ to bequeath their principal private residence to another sibling which allows for property to be inherited tax-free irrespective of its value subject to certain conditions. The main conditions are that the beneficiary must have lived in the house that was the sole residence of the disponer for at least three year prior to the inheritance and for six years after the inheritance and must not have an interest in any other house