Ideally you would never have to because you just have the two people come up with their part of the password and then initialise the LUKS partition together. Sorta like a key ceremony

You can also just split the password for a single LUKS into two parts and give one each to the two people :D

Hey, not sure how in depth your linux/docker knowledge is. Please disregard if irrelevant. I would recommend you pick a fixed mountpoint for the drive and set up a systemd service to mount the drive for you (systemd .mount file). Then you add an extra line “RequiredBy=docker.service” (look for systemd RequiredBy) This way the drive always has to be mounted by the system before docker is started and should always be visible before you start a container.

Hope this helps :)