But only the Keeper can deal with the PCNs unless they name you as the driver, in which case, you would have no protection.
Of the two NtK's you've shown us, one is PoFA compliant and one isn't. The one with no observation time is not compliant and so the Keeper cannot be liable, even though they are claiming keeper liability.
The snippet you've show from the lease clause is clear: no parking without a licence. There’s no implied right to park, and the refusal to grant a licence—even if unreasonable—doesn’t create a defence in contract law.
The driver has no contractual right to park, and the lease explicitly prohibits it without a licence. In other words, you're screwed as far as I can see.
However, even if the lease prohibits parking, NSGL must still comply with PoFA to enforce charges against the Keeper. If they don’t, the Keeper can’t be held liable. Each PCN must stand on its own legal footing, regardless of the lease clause.
The lease clause is a legal hurdle, not a death sentence. As the driver, your best hope lies in procedural flaws in each PCN.
I don't quite understand your mentioning of "NSGL have not followed POPLA protocol". I also don't quite understand the relationship between the driver and the Keeper. If the Keeper is not a resident, then how are you being informed about the PCNs? Have all the PCNs been postal Notices to Keeper (NtK) or are some windscreen Notices to Driver (NtD)?
Because of the problem with your lease, I don't think we can help you very much here and you may want to seek advice elsewhere on how to challenge or dispute the terms of your lease. One hope you may want to explore is whether the contract between NSGL and the management company or the landlord is valid. You would hopefully get a view of that if you were to appeal to POPLA. Certainly if it ever goes to court, you can put them to strict proof of a valid contract to operate and issue PCNs at the location and that that permission flows from the landowner.
For now, based on the two NtKs you showed us, it is the Keeper that is the only person that can deal with them. One is problematic and the other is easily defended. If the Keeper transfers liability to you as the driver, then you have to deal with them and you would be liable for both, irrespective of the PoFA failure in one of them. You could defend on the basis that no observation time means that there is no evidence that any contract was entered into by the driver.
It's all a bit FUBAR.