If you think about it, if its on a P2P network, torrent whatever, anyone in the world has access.
I would guess that once it leaves the household where the physical copy resides as a digital copy via P2P, its considered pirated material regardless who is receiving it.
So, if being shared via the web, Pirated material and subject to the copyright laws. And any internet sharing/downloading can be tracked and recorded and easy to spot.
If it remains in the household, its personal use and no attention drawn to it. Since it would be legal to this, no will come looking nor need to.
Or at least, thats how I would think they would do it.
In all honesty, I don't really think they care if you loan your sister something or other family member/friend.
But distributiong to the masses freely or for profit is what they want to stop.