How to deal with a split when he won't move out?

[owlexpress]

So I am the daughter in this situation. My mum caught my dad having an affair earlier in the year. Initially claimed it was over, then she caught him again. They're married, early 60s, own their house. He's now in a relationship with this woman but still living in the house with my mum. It's been going on for about a year now, and I can't get my head around how he can do this. As if it's not bad enough to cheat on your wife of 40 years, he's not giving her the opportunity to lick her wounds and move on. He's refusing to move out and insists he doesn't want to sell the house. My mum has seen a lawyer and seems to think she can force a house sale fairly soon. It's obviously a sensitive topic and we have a tricky relationship, so I find it hard to ask her the specific as it just ends in an argument. Can anyone clarify? Maybe I should have posted in legal. She's started looking at houses for sale and I guess I just want to manage her expectations, as I'm not sure what the legal barriers are, and even if she can force a sale next year, it's unlikely she'll be in a position to offer on a house any time soon?

A so.icitor is the best person but yes, ultimately a judge can force a sale. It could take a couple of years though. Can she rent somewhere meanwhile if your dad won't go?

He would be advised by a lawyer not to move out, although a sale would need to happen once financials were agreed.

A sale can be forced if he doesn’t agree. It won’t be quick, as you say.

@Doggymummar Thanks for replying. I should also have mentioned we're in Scotland, if it's relevant to the legal issues. They both retired recently which makes it even worse, so she has no money coming in (other than a tiny pension). Some shared savings, tied up in ISAs.