There are potentially three separate taxes involved.
Capital Gains Tax - if your mother is disposing of a property that is not her principal private residence. It makes no difference if there is a price tag attached - it is taxed at market value, if applicable. It does not appear to be applicable.
Capital Acquisitions Tax - you are acquiring a large asset, as a gift, and you may have to pay tax on some aspect of it.
Stamp Duty - if you are a First Time Buyer, you may not have to pay any stamp duty.
Will your brother object to the transfer?
I suggest you need to talk to a solicitor who will go through the issues in detail with you. They may well propose that you talk to an accountant also.
Your mother should also be independently advised. Transferring an asset of this magnitude is a major step and should not be done lightly.
mf