OK, €250,000 @ 1.15% over 20 years gives repayments of €959 per month
These are the same repayments as €170,000 @ 4.5% over twenty years
So if the house is worth €150,000 now, it could be argued that the true negative equity is €20,000.
If he has the income to support mortgage repayments of €959 a month on his own, he should be able to get the mortgage and deeds into his own name.
See how he gets on with his application to ptsb.
You are right, his current partner would be stupid to add her name to a mortgage in negative equity. But people do stupid things.
If ptsb don't agree, then you should reach a side agreement with him that he takes full responsibility for the mortgage and you renounce all claims on the house. The problem for you is that if he defaults on the loan at any stage, you would still be liable to the bank. Also, if you try to buy a house in the future, the existence of this mortgage would count agaiinst you.
If ptsb refuse him, would your income be high enough to take over the mortgage and deeds in your own name?
Brendan