Let's untangle this.
You are in a good position on your mortgage
€368k @ say 1.5% interest is €500 per month. This is the real cost of your accommodation, which is very low. The additional €480 per month is slowly paying the capital down off your mortgage.
You have €50,000 savings, so you are in no danger of falling into arrears or losing your mortgage.
Keep your financial affairs completely separate from his.
Your husband should apply for a voluntary sale and write off of the shortfall
The rent won't cover the repayments.
He doesn't seem to have the skills required to be a landlord
He will be a long time recovering the negative equity - prices have to rise by 150%
His income of €18,000 doesn't allow him to make up any of the shortfall
Step 1 - apply to sell the house by voluntary agreement. Assume that they agree.
Step 2 - sell the house
Step 3 - Ask the lender to write off the shortfall of €175,000. They will refuse
Step 4 Apply for a Debt Settlement Arrangement which would write off the shortfall over a very short period of time - one year -
if they veto the DSA...
Step 5 He applies for bankruptcy.
The lender's attitude
The lender will do their best to involve you, but you must steadfastly refuse to get involved.
If they refuse to allow him to sell the house, then he should apply for a Personal Insolvency Arrangement which would involved selling the house.
Again, if they veto this, he applies for bankruptcy.
You might consider...
If they agree to the voluntary sale of the house
you might agree to making a very small contribution in exchange for writing off the shortfall
Absolutely no more than €10,000.
But keep this up your sleeve. You should argue that you have already paid €20,000 out of your money to the bank and you will be paying nothing more.
you might agree to making a very small contribution