The sad reality is that your mortgage is completely unsustainable.
Even if they were to switch you to interest only, you would pay €350k @4.5% which would be €16,000 a year.
If they warehoused the negative equity and left you with an active mortgage of €220,000 @4.5%, interest only, you would pay €10,000 a year or €825 a month. You can't afford that either.
On top of that, you have an unsustainable investment mortgage.
You should enter into discussions with Pepper about a voluntary sale of both properties and a write-off of the shortfall.
If they don't agree to this, then you should agree a voluntary sale of your investment property, but refuse to sell your home, as you have no alternative.
If they do agree to write off the shortfall, you should surrender your home.
You could also agree to the voluntary sale and seek to have the shortfall dealt with through a Personal Insolvency Arrangement or bankruptcy.
Brendan