If your brother sold his family home, and if his share of the equity was at least €80,000 (share of equity calculated on the basis that the primary mortgage, if any, is deducted from the selling price) then he would have to pay over €80,000 to the bank.
If he paid over the full €80,000 he could then sue his ex-partner for 50% of the debt.
Your brother should bear in mind that the debt is increasing at 8% per annum.
I am unable, in a public forum such as this, to comment on strategies of individual banks. However, I can generally say that it is practically impossible to enforce a judgment mortgage on a family home where it is co-owned with a spouse.
I would suggest that this may the time to try and do a deal with the bank. Once AIB "floats" back onto the stock exchange its existing policies could toughen etc.
Jim Stafford