I presume that the investment property is in your joint names? If not, one of you could go for a PIA or bankruptcy.
Net income |€3,350
Minimum Reasonable Living Expenses| €2,268
Home loan repayments|€1,015
Available for creditors|€67
You need to do this calculation formally and show the results to KBC.
You are effectively insolvent, so you have a few options
1) Ask BoS to put you on interest only and use the €400 extra per month to make up the shortfall with KBC - I expect BoS would refuse this.
2) Pay just the net rent on the investment property - For the moment, this is the only option you have. Write to KBC telling them that your paying only the net rent until further notice. Alternatively you will agree to a voluntary sale. If you are paying the full interest only, they have no incentive to address the problem.
3) Go for a Personal Insolvency Arrangement
4) Sell the investment and go for a Debt Settlement Arrangement
5) Sell both properties and go to the UK and both of you go bankrupt.
6) Try to do a voluntary deal with KBC
If and when you get a job again, you will be able to meet the full interest on your investment property while maintaining the full repayments on your home. This argues for a Personal Insolvency Arrangment or bankruptcy now.
If you can get a fresh start without any debt (but also without home ownership), when you are both earning, you will be able to build up savings again.
You don't tell us the value of your home or the interest rate , which are critical. If it's not in huge negative equity and you have a cheap tracker, then you should try to retain it. If it's in huge negative equity and it's a SVR loan, you should be happy to get rid of it.