How to switch SSDs in Macbook Pro Retina 13'' Late 2012 and Macbook Pro 15'' Mid 2009?

I am using a **MBP Retina 13'' Late 2012 (MBP10,2)** (I know, very old, but still running great and very smooth with the latest Ubuntu) with a **121 GB APPLE SSD SM128E** – which is quite small, particularly considering that I have a macOS/Ubuntu dual boot setup and some audio editing software... Also, we still have my friend's old **MBP 15'' Mid 2009 (MBP5,4)**. Ages ago, we upgraded it with a **500 GB Samsung SSD 850 EVO** which still works fine. Now I'd like to switch the SSDs of both computers. The 2009 MBP is still used sometimes as a 'backup' for some older offline software and its DVD drive, but 121 GB would be totally sufficient. I know there might be problems with physical compatibility of the SSDs, but all I found online seemed a bit ambiguos so I'm not sure: **(How) is it possible to exchange the SSD drives of these laptops?** I found this question (https://apple.stackexchange.com/questions/153414/macbook-pro-retina-13-late-2012-ssd-replacement-putting-in-a-sata-2-5-ssd-dr) which gave me the impression that even 'MBP Retina 13'' Late 2012' is not specific enough to be sure about the SATA type or something, so now I am confused how to definitely find out which one I have. Also, I couldn't find out which plug type the 2009 MBP has. If they are not compatible, I might try an adapter for the 2012 MBP, but is there also an adampter 'vice versa' for installing the 121 GB SSD in the 2009 MBP? Anyone have any experiences with that or tips regarding compatibility/adapters? If it's only possible with two adapters: Would you recommend it?