Could someone describe porting over the phone to me ?

family plan of four lines on at&t, devices are all unlocked. got the $35/4 tmobile one promotion signed up, got the 4 sim starter kits already. anxious about calling in to port.

anyone describe what happens ? how they port 4 numbers from one carrier to another ?

also i don't have a landline or an extra phone to use. i'll be making the port on one of the four phones. won't i be disconnected ?