He can't appeal anything, that boat has sailed for the moment and whether it will return to port is unclear.
OP, in order to speed this along I suggest you and he park '.....without consent..', it's hopeless based on what you've said. Of course he gave consent: he left the keys there so that the vehicles) could be used as and when necessary.
This is about procedure and as already stated we need documents. We also need to know how and when correspondence with authorities was sent. So far this matter has NOT been passed to bailiffs(the sums owed would be higher) therefore we're left to assume that Orders for Recovery have been issued, and prior to these Charge Certificates.
IMO, if any correspondence was sent to the authorities prior to the CC and OfR notifying them that the owner was in prison - which in our parlance means that the authorities may not use the address supplied by DVLA - then the critical docs were not served and Out of Time submissions, or in-time if applicable, should succeed. It's possible to mange one's affairs from with a prison(but I don't speak with personal experience!).
We do not need to know about the contraventions themselves, we need documents, yours and theirs.