I need one SD card per device for it to run, right?
Yes, each device has its own controller board.
Thanks for the clarification.
However, on every page and occasion, you are mentioning SD Card. I would assume this is full-size SD Card required. And now we know that micro SD is required. I have full-size SD card in my cupboard and I thought it will be just fine, so I purchased another microSD card for second unit (I have SD adapter). I was lucky with that purchase, now I know that

My card will work. But I need another one now :|
I thought I will be OK with SD card and microSD->adapter card.
Can you please correct that for other people.