We were in your situation about 7 years ago.
Mortgage was £2700, we had school fees, nursery fees, debt, you name it we had it. The stress was unbelievable and even thinking about it today makes my chest tighten.
We had two kids under 5 and both of us were working full time. My mother then suddenly passed away and I was on my knees mentally.
So we took a deep breath and we sold the house and moved into rented to figure out where to go next. We sold it for exactly the same price we bought it for which was very lucky.
I remember the day we moved into the rented house, the sun was shining and the church bells were ringing. I just couldn't stop smiling and I felt like I could breath again. It was so liberating.
We ended up making a radical change to our lives. We move to Devon and renovated a small cottage and now live mortgage free. Kids go to local private school and the monthly bills are manageable. My husband works part time and I'm now a SAHM. We have a small amount of debt from the renovation, which is now a priority and will be wiped off next year. Plus we have a good investment portfolio now and a passive income stream as well.
We did a complete reset of our lives and we couldn't be happier.
When I used to look at big houses or large family homes, I used to view them as something I really wanted. Now when I walk past them or visit a friend's new place I'm mentally adding up the bills and think no way would I want to go down that route again!
You can get out of this situation. You need to sit down and come up with a plan on what to do. In your shoes, I would look to sell and get out from under the mortgage.
Good luck