Sorry to hear about your position.
What is the market value of the property? You have mentioned you have a mortgage of 90k and you are prepared to give back the apartment to the bank, so that is effectively selling it at 90k!!. My guess from your information is that the property is worth more than 90k.
What is to stop you selling it for 90k Euros or 80k Euros?? Everything (and I mean everything) sells for a price. The squatters are irrelevant and so is the lack of fixtures in the apartment to selling if the price is low enough.
You then walk away with the apartment legally sold.
So what were you recently advertising as the price of the property?
The property has been on the market for €95 but had no interest in the property. I cannot afford to let the property go for less as I do not have the income or savings I once had. Due to a serious back problem I am now surviving on disability. The main reason that has stopped me moving to Spain.