I understand what I am attempting to do here guys
I pay £2.49 presently for 200GB family plan but don't want to jump to 2TB for £7 per month as that's way more storage than I need or want to pay.
I'm on Android now so it's just my wife continuing to take pictures that get uploaded to iCloud
Amazon photos and Google photos have options to upload unlimited medium quality images which suits me much better but won't work on my wife's phone as the iCloud photo storage is the default option and turning it off will just fill up the device
Basically I want the best of both worlds and am happy to put a bit of work in to get there