Please confirm whether the PCNs you have shown us are copies of the Notice to Keeper (NtK) issued to the hire company in their name or are they the Notice to Hirer (NtH) that was sent to you by PE after the hire company transferred liability to you, the Hirer?
You can only respond to the PCNs if they are in your name. It is not established, from what you've told us, that liability was correctly transferred by the hire company.
The hire company and PE do not know the identity of the driver. The only thing known is that the Hire company is the Keeper and you are the Hirer. The driver is the entity that is liable and there is no legal obligation on the Hirer to identify the driver.
As PoFA has not been invoked, there can be no Hirer liability. So, are those PCNs that you have shown us, addressed to the Hirer or are they simply copies of the NtKs issued to the Hire company?