First redact your name and address, and VRM from the letter you have posted!
Were the PCNs incurred in Scotland? Have you replied to any previous letters from Smart or DCBL - if so, what did you say?
Assuming that the PCNs were issued in Scotland, and you haven't identified the driver, then you can ignore; there's no keeper liability in Scotland. They might try it on as the total is over £500, but it should be easily batted away.