With point 1, not completely sure what you mean with this. If the sharee wants to play a game, that specific game needs to be installed on the sharer's PC? So The sharer and the sharee needs to have the exact same installed library?
Sorry, I missed your post earlier. From the FAQ:
I share a computer with another Steam user and want to request access to their games. What do I do?
If another Steam user has installed a game on your shared computer, you can log into Steam on this device using your own account and send a sharing request. To do this, visit your library, where you'll see your friend's installed games. Select the Play button to launch a request form. Once sent, this will send an email to the account holder.
The access request, if approved, allows the secondary user to access your entire library, but as per the above, said request can only be sent if you had installed at least one game on their machine.