No they don’t. They put it into a machine or swab it
Depends on the airport. We went on 4 planes with our 2 month old on our holiday. Some they opened tested and kept for what seemed like ages, some just scanned them, some just let us walk through
No they don't open it, it goes through a special scanner
You can click and collect to boot at airport then get it after security
They will check with their scanner