No, they won't need a solicitor. They can represent themselves in Court, it really is not rocket science.
Ultimately, the claimants will need to justify the claimed amount to the satisfaction of a Judge - let them take you to Court IMHO. Just reply to the letter stating that you have no offer to make and that they should refer the matter to Court.
I have represented myself in Court for the last 2 years, I am quite happy to explain how it all works - e-mail in trust.
The kind of person who doesn't open letters (and we all know that there have been lots of letters, both from her insurers and latterly the MIB), who simply hopes things will "go away" probably doesn't have the mental capacity to successfully represent themselves in court.