OK, firstly I think it would be ok to presume that your Mother wrote that letter 'under duress' so it is not automatically and admission.
Am I correct that nothing has been paid since 2007?
Personally, I would totally ignore them, open their letters as they arrive and only take notice if and that is a very big if they threatend Court Proceeding.
I am also fairly sure, that, having said that, as there is already a Judgement in place, they cannot issue further CCJs, and in any event, it would be the Original Creditor that would now have to take up the sword to try and enforce the CCJ. A judge would be extremely unlikely to allow this given the period the OC has been 'inactive' on this Account.
Others will be along but hopefully their advise will be similar.
Please tell you parents not to worry, keep on here for advice as things move (or not) along.