So I might go for these speakers
Is there such a thing I can wire them into which will connect to an ipad/iphone via bluetooth to play the sound?
Simple answer to your question is yes - there are huge numbers of products on the marker that do what you want to do. You could buy a very basic Bluetooth adapter off Aliexpress for ~NZ$4 or easily spend $80 for one locally. Without knowing your actual requirements it's hard to make a specific recommendation.
The Echo Dot smart speaker can also function as a bluetooth speaker and has a 3.5mm out jack you can use to connect it to your stereo.
I do this sometimes so I can bluetooth from my phone to the stereo. Another option that's not crazy expensive if you don't mind smart speakers.
I disconnect it the rest of the time so I can use it for alarms and weather etc.
If you do go down the BT speaker path I highly recommend these:
Note: Can be got for less on sale.
I purchased 2 which can be hooked up in stereo - they sound really good (and I say this as someone who is kinda fussy with audio gear) - and they are way cheaper than name brand options.
Start looking thru these search results - https://www.aliexpress.com/wholesale?SearchText=bluetooth+tpa3116