Before you get anti-depressants, get a plan.
Ask a local estate agent to provide a written valuation of the house; deduct your mother's majority share and split the remainder into two equal parts to obtain a ball park figure that you will need to to pay off buy out your dh.
You'll then need to source mortgage lenders to see if there's any way you can raise the necessary funds.
Do your 3 ds's have their own bedrooms? If so, needs must when the devil drives, and two of them will need to bunk in together so that you can have your own bedroom with a proper bed.
This could be the catalyst for breaking the news to your dcs - although surely they've noticed that their parents' marriage is on the rocks? You'll need to reassure them, and your dm and, from the sound of it, your db, that the fact that your marriage is over will not make any material difference to their living conditions.
You've effectively been separated for 2 years, and now it's time to file for divorce. You don't need a solicitor to start proceedings as you can do it online, and maybe when the papers are served on him your dh will buck his ideas up.
If you've committed to attend the forthcoming wedding as a family unit, it may be politic to wait until the event is over before announcing your changed circumstances to all who need to know.
Should your dh 'turn nasty' and threaten you in any way, call the police and have him forcibly removed if necessary - and follow through by seeking a restraining order.
The above is purely practical advice - I'm not without sympathy for your dh but, from what you've said, it seems that you're the mainstay of your extended family and, therefore, your emotional and physical well-being is paramount.