From examining section 30 of the Land and Conveyancing Reform Act 2009 it can be seen, the law in on the side of Shane Kirwan. The mortgage is void ab initio and can be proved thus. The fact of the matter is that the bank erred in law in issuing a mortgage to Shane Kirwan, when the security for the mortgage was the deeds of the family home, which, at that point in time, was in co ownership with Mr Kirwan's now deceased Father, without his Father's written consent. Mr Kirwan's Father did not unreasonably withhold his consent, on the contrary, he was never even informed by the bank that there was now a charge on his property. Therefore, the provisions of section 31 (2) (e) of the said Act, do not apply and cannot be relied on by the bank. It can be seen that the law is very clear on the matter.
So, the simple answer to the poster's question is, yes, the mortgage is void and cannot be enforced.