To share your home, use the Home app to manage home members. The family member you invite must have a Gmail account or a Google account associated with the email address you invite. Once added, your Nest Protect should show up in the Nest app for them as well if they sign in with the account you invited.
Due to inactivity, I'll go ahead and lock this thread in 24 hours. Feel free to start a new thread if you need assistance with your Nest devices and we'd be glad to assist you further.