Ruam Kan shows what's on the streaming services you already have and opens each title in the right app. You can use it without an account; signing in keeps your profiles and lists on every device.
There's no password.
Open the invite link first, then sign in, then press Accept. You land in the right household, or are added as a friend.
Nobody types a password on the TV.
Settings > Account > TV PIN. With a PIN, a shared TV asks for it before opening your profiles, so others can't use them.
Nothing is shared until you switch it on in Settings > Sharing: your list, what you've watched and your stars each have their own switch.
Email support@ruamkan.com. More answers on the support page.