Can all Steam games be shared with friends and family?
No, due to technical limitations, some Steam games may be unavailable for sharing. For example, titles that require an additional third-party key, account, or subscription in order to play cannot be shared between accounts.
Can two users share a library and both play at the same time?
No, a shared library may only be accessed by one user at a time.
When I authorize a device to lend my library to others, do I limit my own ability to access and play my games?
As the account holder, you may always access and play your games at any time. If you decide to start playing when another user is already playing one of your games, he/she will be given a few minutes to either purchase the game or quit playing.