@Birdy1700
It depends on what kind of Nest Aware subscription you have. If you still have the old 1st gen Nest Aware subscriptions, which are per-camera, then you would need to purchase 1st gen subscriptions for each camera. If you have the newer Nest Aware or Nest Aware Plus subscription, which covers all new and old cameras in the same Google Nest "home/structure", then all you should need to do is to add your new cameras to the same Google Nest "home/structure" on the same Google Account. That's how ours has worked for years.
However, getting video event history only for the most recent 3 hours is a characteristic of the newer 2nd gen Google Nest cameras and doorbells that work ONLY in the Google Home app. Without a subscription, the older 1st gen cameras and doorbells that work in the Google Nest app provide only photo snapshots for the most recent 3 hours. At least, that's what Google Nest's documentation says:
https://support.google.com/googlenest/answer/9681538?hl=en
