I believe the intent of the question is they all have the software on their computer concurrently.
In that case, almost assuredly illegal.
Some software manuf. allow a small number of computers to utilize the same copy. In our office, we have a few programs that the provider allows to be installed on up to 3 computers.
I doubt any of the game producers allow multiple user installs.
The general rule is, you must remove it from your computer when you sell or give away the disc.
Music is the same way. You are allowed to make copies of those CD;s but if you were to give somebody else the original, youmust either destroy the copy or give it with the original CD.

