This is a difficult one.
You are not paying anything. You are not able to afford to pay anything. So it doesn't much matter to you what happens the house and the mortgage.
So I see no advantage to you in facilitating the repossession of the house. Quite the opposite in fact.
It's likely to be the cheapest option for him and for his partner to stay in the house and pay what they can on mortgage repayments. Presumably the cheapest option for him, is good for you, in that if he has cheap accommodation, he has more money available to pay maintenance. Likewise, if he has a decent house to live in, he has a place to mind his children.
Over time, the house may rise in value and clear the negative equity, which would be good for you. Or maybe his financial position will improve and he will be able to take over the mortgage in full.
If the house is sold, then you will be jointly and severally liable for the shortfall of €95,000. This means that it will hang over both of you for a very long time. It's not €47,500 each. It's joint and several. In other words, if you pay off half of it, you still owe the other half.
The temptation for most people in these situations is to make life as difficult as possible for the ex. Don't.
Now let's look at it from his point of view...
You are paying nothing towards the mortgage but you are still an owner of the property. If he keeps up repayments, eventually, the negative equity will disappear by a combination of capital repayments and price rises. Let's say that after 10 years, there is €20k equity. You will still own half the house. He will need your permission to sell it or get a new mortgage. So he probably wants you off the mortgage and off the title deeds. I don't really see what he can say in the email to you , except to ask you to help him to keep the house by not facilitating the repossession.
It's possible that his new partner might want to buy your share of the house and take over your share of the mortgage. If that happens, you should grab it with both hands. It's unlikely that the bank would allow this, unless his partner has a lump of cash with which to pay off the arrears.
The court is very unlikely to grant the lender an order for repossession
If you ex wants to keep the house, he will get to keep it simply by paying something to the lender and by showing up in court.
If he pays nothing and doesn't show up in court, and you do show up in court agreeing to the repossession, there is a small, but very small, chance that the court might grant an order.