Unfortunately, I think this has arisen because you didn't understand your mortgage terms. Your solicitor deals with the house purchase for you, but she doesn't arrange the mortgage - she checks you have one arranged, and then completes the legal paperwork the mortgage company requires to lend you money for the purchase.
If you had used a broker, s/he would have talked you through the terms of various mortgages, and highlighted conditions like this. There are other products that would have allowed you to have a joint mortgage with just one salary, as others suggest, but you didn't pick one of those. With hindsight, it probably wasn't appropriate for you and your dh to pick one in your dh's sole name... But it isn't your solicitor's role to help you understand or choose a mortgage: if you don't use a broker, you take on this responsibility yourselves.
Once you have chosen a mortgage, you are bound by its terms and conditions. Refusing to sign the occupier's consent form wasn't a viable option - the mortgage company wants to ensure that they can force a sale if your husband fails to pay the mortgage in his sole name and insists that you sign a doc agreeing to leave in those circumstances.
By refusing, you put your solicitor in an awkward position. She has no choice but to inform the mortgage co, because signing that form isn't optional - it's a key condition of the mortgage you chose, and of every mortgage in a sole name.
It maybe would have been kind for her to explain this to you better. But it sounds like you have been blaming her for something that wasn't her fault, so she perhaps isn't feeling kind, and I imagine communication between you isn't very good.
As far as I can see, if you don't want to lose your deposit and want to try to keep this sale, your options are as follows:
1a. Go to your solicitor and apologise. Explain you had misunderstood her role and now realise it wasn't her responsibility to help you understand your mortgage, and that with hindsight, you think you maybe should have used a broker. Ask her if she is prepared to help you try to save this house purchase now. If so, go to step 2.
1b. Find another solicitor who is prepared to help you try to save the purchase.
- Decide whether you are going to (a) stick with this mortgage - in which case you must sign the form - or (b) switch to a new mortgage in joint names.
If (2a) you may be able to protect yourself with a signed agreement between you and your dh, but you need legal advice, because this wouldn't undo the fact that you will still have to promise the mortgage co that you have no claim on the house if the mortgage isn't paid.
If (2b) get a broker to help you find a new mortgage that suits your requirements. You will have to pay fees again, get another valuation, and perhaps borrow less or pay a higher rate. A broker may be able to help you negotiate and get a new joint mortgage with the same provider, which would save you time and money.
If you can't borrow enough via a joint mortgage, then you really have no option but to sign the form or lose the purchase.
- If there is any delay at all, ask the solicitor to talk nicely to the sellers' solicitor and explain there has been a problem with the mortgage but that it will be resolved and you are still keen to proceed. If you have already exchanged contracts and set a completion date (and it sounds like you have) then you are legally obliged to complete by that date or lose your deposit... But if the sellers want to save their sale to you too, they might not hold you to that...
I hope you can resolve this. Good luck.