Husband still sharing mortgage with his ex

My husband separated with his ex-wife and moved out of their house just over five years ago now. He and I got together six months afterwards, my husband asked me to marry him and asked her to start divorce proceedings so we could do so.

I couldn't convince him to see a solicitor to sort out the details of their financial arrangements, so all the details were arranged by her solicitor who put some wording in that meant my husband should remain on the mortgage until she was in a position to be able to take it on herself. He hadn't realised the implications of this as he'd agreed verbally with her to just stay on it for a couple of months after the divorce while she got something sorted out. She had a partner living with her at the time. We presumed she'd re-mortgage very quickly with him.

So, back then, believing I would be remortgaging my property with my husband shortly, and that we would be consolidating our debts as I have my own mortgage, we spent money on credit cards to pay for the wedding, a holiday. My husband wanted to try for a baby and I agreed, thinking we would be financially secure (I have two children from a previous marriage living with me already) We ended up having twins two years ago which brings the children living in our house to four. We had to get a loan to buy a larger car to fit all of us in. Could only afford second hand and it broke down in the first couple of months we had it, costing us a couple of grand. We also had to get a loft conversion because my house wasn't big enough, I ended up having to re-mortgage on my own for that.

Anyway, more than three years from the divorce now and more than five years since he actually moved out - my husband is still on his ex's mortgage, and we are really struggling because we can't consolidate the debts we presumed were temporary and we've got four children. She is childless but self-employed, following her dream job, but can't afford to take on the interest-only mortgage on her own. She gets angry and abusive at my husband, at our first solicitor, at me when it has been brought up. She lied to me and told me that her and my husband had planned her staying on the mortgage together all along so that she wouldn't lay claim on his pension. He says this is lies

I'm not sure what help I expect to get from you guys, it seems a pretty hopeless situation!