Do please give us chance to reply! This is a busy forum and I do this as a volunteer alongside my full time job.
There is an argument to be made that ParkingEye's PCNs do not comply with the requirements of Schedule 4 of the Protection of Freedoms Act, which would allow them to recover the charge from the keeper of the vehicle. If it does not comply, they can only hold the driver liable, and they don't know who that is. Opinions vary on this point - my personal view is that going to court on that point alone, without any other defence, would be a risky tactic.
Neither ParkingEye nor POPLA would accept that argument, so you'd need to be prepared to potentially argue it in court.
One thing you should definitely try is to speak to the management of the venue you were visiting, to see if they will intervene. I don't mean to sound blunt, but you could seek to play off the fact you were there as a carer for someone who is presumably disabled and/or vulnerable in some way.