It's about affordability. They want to lend, a Garda is a good bet. You have not given us any idea of how much money he has, how much he wants to borrow and how much is the property.
You asked a specific question about legal separation. How is that progressing, is is amicable, legal? Because it might be best to wait for that to be sorted first. They are surely entitled to some equity in the family home. But I can tell you that in court the decisions are impossible to decipher or predict and my relative has been congratulated by many professionals for getting equity as apparently it's very unusual. It came at some mental cost though. My own solicitor was surprised at the court judgment.
The separation is very much in early stages and unclear what each party may want from it but it's highly unlikely that an early agreement will be reached.
I agree that trying to get equity actually paid can be very difficult if there's no incentive for the person in the house and it could drag out years.
Im not sure if it may be an option to hand over the house in lieu of ongoing spousal support , and to use existing savings for the spouse to buy him out. But that may leave both of them in a poor position with him not having enough deposit and the ex spouse trying to run a large house on a low income. Realistically selling the house and splitting equity, agreeing ongoing support from pension may be most appropriate route, to ensure its sustainable but with any separation, emotions run high. And obviously he needs to understand how any maintenance payments would impact mortgage application.
He is much higher earner and mortgage broker indicated he may be able to borrow 250k but he needs to get everything in order and show significant savings. He would also need to have legal separation sorted before he could draw down mortgage
Right now there's approx 100k savings. House is worth I'd say 600k give or take and mortgage free.
600 (equity) + 100 (savings) + 250 (mortgage) gives about 900k after costs, in which in my mind should allow purchase of 2 properties, which could be a 2 bed for him and 3 bed for spouse and adult college gking child, for example.
There may also be inheritance coming to his spouse. And lump sum of 100k (very approx ) for him at retirement.
Looking at the figures a house sale may be needed but that could take years and years..
If he could handover house in lieu of maintenance then would lender take into account his future lump sum and pension??
Then separately ex spouse could decide if they want to stay in bigger house or sell and downsize..