It’ll be messy enough. Your sibling will have significant CGT bill. You’ll have a CAT liability of 33% of €150k minus the €33,500 Group B threshold (if still intact) minus the €3k Small Gift Exemption. There should be credit for the CGT against the CAT.
It might be better though to just leave it and inherit it; no CGT on death and the potential to inherit the share tax-free via the Dwelling House Exemption if you cohabit, but the flip-side is that values should increase over time.