From the blog post (for what it's worth, I think it's a good idea):

>Six accounts, one price. Every YouTube TV membership comes with six accounts, each with its own unique recommendations and personal DVR with no storage limits. You can watch up to three concurrent streams at a time.

https://youtube.googleblog.com/2017/02/finally-live-tv-made-...

Presumably that you can add up to 6 Google accounts (i.e, your family members in the same household) to the plan for the listed price. They have a similar deal going for Google Play Music, Netflix has it, etc.