Depending on when you read this, Steam Family sharing is either in beta or finally released to the public. Either way, if you're going to share your Steam library with family members after years of building your library, you might want to limit which games they can actually see!
Family Sharing in a Nutshell It's been possible to share your Steam library with family members for many years, but the way it worked is that you shared your entire library and if you started up any game on your PC, the other user would be kicked out—even if they were playing a completely different game.
Steam has revamped this system with a feature called Steam Families where you can share games on an individual basis, and as long as two people aren't trying to play the same game, everyone can play concurrently.
We've covered all the most important facts about Steam Families already, so I won't repeat it all here, but before we get into how you can control what people see from your library, you need to enable Steam Families, if the feature is still in Beta when you read this.
Every participant needs to go to Steam > Settings > Interface > Client Beta Participation and ensure that "Steam Families Beta" is enabled.