I would start by redacting your postal address, you probably don't want that to be published on the internet. As for the NTOs, go online and make representations as follows (you'll have to do it twice, once for each PCN).
Dear London Borough of Brent,
My vehicle was parked prior to the suspension signs being installed, please look at the second to last entry on the Serco suspension sheet log dated 14 April 2023. As my vehicle was parked prior to the signs being installed, and the signs were only installed three days prior to the suspension coming into force, the alleged contravention did not occur.
Obviously if a more reasonable amount of notice had been given I would have seen the signs and I would have parked elsewhere.
Yours faithfully,
Get a screenshot of the confirmation screen.