From what you say, I don't think you've done anything wrong but you will need to explain it all in detail, backed up with your papers and (if necessary) evidence from the other people involved.
It would be best for you to go to the interview with a representative. If you can do so, find a solicitors firm that deals with this sort of issue on legal aid (as you are on benefits you should be entitled to that). It probably means finding a firm with a legal aid franchise for welfare benefits work, or possibly for criminal work. You could start with your local CAB as, if they can't help you themselves, they may know of such firms.