There are two strands to the house and mortgage. What you can achieve legally, and what you can afford financially. There's nothing to stop you running some numbers with a mortgage broker to check your options, financially.
Is this correct?
£330K value, £85K left to pay, over approx 12 years, £715 a month?
(Btw that's 3.1% interest which isn't way over the odds, but I think is higher than it could be - there are 10 year fixes at your LTV of 2.49% which is £690)
I think financially you would struggle to get an £85K mortgage - if you received 100% of the house in the settlement. It sounds like because of your SN son, increasing your work hours would be unlikely. So you need a lender that includes tax credits and maintenance. They exist but are limited. And I think with maintenance, they want to see 12 months history of payments - you really need a specialist broker for that though!
Option 1: you get the house entirely - and take on the mortgage. You need a broker to work out if you can get an £85K mortgage. (option 1b
can you reduce that £85K with savings, other assets...)
Option 2: agree as high a % of the equity as you can, sell up and buy mortgage free with your amount (cheaper area, downsize...) Maybe suppliment with mortgage - but see above on affordability!
Option 3: (especially if you don't get expect the lion's share of the equity)
look into a Mesher Order, where you stay in the house and he pays the mortgage til a specified date, usually youngest turning 18. Be careful though - if you can't afford to buy him out it's postponing the issue. I think it works well for women who expect a change in circumstances in the intervening years - e.g. Children moving out so costs down and practical to downsize.
The thing is, you can't really know your options yet. You need to start financial disclosure. That pension is critical! The higher the pension, the higher your chance of more house equity even in an overall 50/50 split (and I think you have a good chance of more because of the dependent children)
In the meantime, DO NOT PANIC.
The thing is, it's not in his interests to default on the mortgage - it'll screw him up for credit worthiness. So don't allow yourself to be rushed. Get all the info, and legal advice.
In his position I would give up more equity over being stuck with a Mesher Order. He's not a high earner so he won't get another mortgage whilst he's on the Mesher (and would get hit for more SDLT I think!).
As well as wishing you luck, can I just add that although I am opinionated
I am not a lawyer - so please please don't take anything I say as fact, or correct for your situation. You could post in Legal - there are some family lawyers there!