I'm so sorry this is happening to you, so sad and scary.
I might have missed something, but surely the clearest way forward is:
Sell the house - you each get your £85k equity out of it.
Flats near you with space for a parent plus DS are £150k, you say. So no stamp duty, which is great. Set aside £5k of your equity for moving fees and costs, and you are looking at needing a mortgage of £70k to afford a flat for yourself and DS.
On your salary of £27k, you should be able to get a mortgage of around £90k, so £70k is totally doable.
£70k at 5% interest over a 15 year term, to pick a reasonable-ish figures out of the air, is a monthly repayment of £554. That sounds reasonable to me; if it sounds high you could extend the term etc to make it more affordable, depending on your age.
And all that without even touching your savings.
So...I think there is a way forward.
I may have mis-gleaned some of these facts eg maybe the £150k flat isn't a two bed price. But there's enough slack in the above to accommodate even things like your new home costing more than £150k, moving costs being higher than expected, etc, especially given you have some savings.
It does mean needing to accept that you have to leave the family home, but ultimately it doesn't sound like you can afford to stay there, which makes sense as it was affordable based on you both living there together. Now you need to live separately, and more cheaply as individuals, so you can both move on. Good luck.