Right, so your DH is a surveyor, not a teacher? How far into his career is he? (I.e. are his earnings likely to rise dramatically in the next few years, or is he already quite established?)
Is your Masters actually likely to result in more earnings potential for you, or are you doing it for your own edification? How much longer do you have? (I.e. is it a part-time degree that takes years and years and years to complete, or do you just have a year left?)
I think you need to start looking at this as 'how I can cope in the short term' vs 'how will I cope in the medium term?'
If you're eating into savings temporarily, but you know your earning potential will increase, it's not a comfortable place to be, but it's not a disaster. Similarly, if you switch to a cheaper mortgage in the short term (but you're adding on extra years etc), it's not ideal, but when things get better, you can remortgage and reduce the length of the mortgage/start making capital repayments again.
I think I'd try to stick out the Masters if financially viable, because it will be hard for you to pick it up again later down the line. However, if needs must... you may need to consider putting it on ice and taking another job in the time you were spending on studying.
In summary... it's all just a bit shit, isn't it?