I assume it would be quite usual for Crew to live together. Most forums, including pprune, place a cookie on the computer enabling the manual logon & password routine to be avoided each time the forum is accessed. So the IP address may tell only part of the story.
It could be a case similar to original car speed camera fines, whereby companies (including Manchester United/Sir Alex Fergusson I recall) and families avoided fines and points as they claimed they could not identify who was driving the car at the time. Nowadays the cameras photograph the driver.