Steam says you officially only get one family per year as its new game sharing feature leaves beta

gamesradar.com:

Steam's new and improved family game sharing feature is now available to everyone, but you'll want to choose carefully which family you become a part of.

Valve introduced 'Steam Families' back in March as a more convenient and feature-rich tool for families and friend groups to share games between one another. The new iteration replaces both Steam Family Sharing and Steam Family View and gives you a single location to access all of the games shared across family members' Steam libraries. 

Steam Families lets you create a family of up to six Steam users and identify each member as either an adult or child. Adults have access to parental controls that'll let you choose what your kid is playing and for how long, and what Steam features they have access to. Adult users will also be able to view children's activity reports and recover lost passwords, invite members, remove members, and leave families, none of which are tools available to child members. The only thing child users can do is play games and request that adults pay for their games, which adults can do through their mobile device or email.

All games in your Steam library will automatically be added to Steam Families for all members to access, although Valve says there might be the odd exception if a developer wants their game excluded due to technical reasons. All adult members of a family will have access to each other's games, but you can only play the same game at the same time if there are multiple copies.

If you are thinking of joining or creating a Steam Family, I'd suggest doing so carefully. Valve confirmed in an FAQ that, once you leave a family, you won't be able to join another one until it's been a year since you joined the first one. Likewise, the spot in a family previously occupied by someone who left has a "cooldown" of one year before another member can join.

Another reason, beyond conventional wisdom, to be super selective about who you choose to link up with, is that you'll be liable for