You have a mortgage of €258,000@ 4%
The interest only on this would be €10,320 or €860 per month.
So it makes sense for you and your children to stay where you are. If you pay the interest only, the mortgage balance will remain at €258,000. Your position will not be getting better and it won't be getting worse.
Tell the bank and your ex this. Your ex will remain on the hook for the shortfall or he will benefit from any increase in the value. If you pay off the capital now, he will benefit from this as it will be reducing his liability.
The bank are giving little or no solutions whatsoever,
That is because there really is no easy solution. The bank can't magic up a solution out of thin air. You split with your ex. You now have two premises between you. That is not the bank's fault.
You took out a loan jointly and severally with your ex. That means that if you don't pay, he is liable for it and if he doesn't pay, you are liable for it.
This was the contract you agreed. Again, the bank lent the money on the basis of two borrowers and not one borrower.
Did you do an agreement with your ex when you bought the house? Did it cover negative equity and splitting up?
Who put up the deposit for the house? Assuming you put it up equally, your husband should pay you €30,000 to be released from the deeds of the house and the mortgage. This is academic if he does not have the money.
What happens when the fixed rate ends? I presume you don't qualify for a cheap tracker if you bought in 2009. Which bank are you with? What is their Standard Variable Rate?