Noticed you were advised to look into MIS. If one of you is employed (assuming you're married) also look into FIS. You can get this if one of you is working more than 19 hours a week. Could make up a portion of the shortfall and put your SFS in a better position. Allowances near bottom...
Don't be so sure that the banks won't write off the debt. Banks want non performing loans off their books and there is no point pursing people who have no assets/income so in those cases banks will have to write off the debt.
Why are you not entitled to mortgage supplement.
You shouldn't just rely on an internet forum, have you thought about makign an appointment with Mabs, apparently they do great work for people with money problems, and it's free. It's always good to get advice elsewhere.