Hi Toad
With an income of €2,000 a month, with €1,000 going on childcare, it seems to me that your mortgage of €390,000 is not sustainable. If your mortgage is not sustainable, then AIB is right not to give you a split mortgage. One of the first tests for a split mortgage, is whether it is sustainable or not.
Is your ex husband's name still on the mortgage and title deeds? If so, then you would need to sort that out. Is he contributing to the mortgage.
Who is the father of your two children? Presumably your current partner and not your ex husband?
With €110,000 in negative equity, there is no way that your current partner should get involved in any way, unless AIB does some very generous deal for you.
I think you should contact the Irish Mortgage Holders Group and get them to discuss your options with you.
I think that you should be planning to go bankrupt. You can offer AIB an alternative along the following lines. Write down the mortgage from €390k to €300k and your new partner to add his name to the mortgage. That would be a sustainable mortgage and would be to everyone's advantage. If AIB says no, you must be prepared to go bankrupt and lose your home.