As for why Lu Chan was chosen.
There is no other reason.
It's simply because Lu Chan is Lu Shouren's confidante, and she is extremely astute. Astute individuals typically have a far-sighted perspective, and wouldn't treat anyone differently just because they aren't inherently part of the Lu Family.
Furthermore, she is aware of East Spring Undying Bone's capabilities, so when I present a tremendous favor, how could she refuse?
Lu Chan's residence is located at the back of the Lu Family, also within the region of the Tier Three Spiritual Vein that is quite central to the Lu Clan Territory. If you go further inside, you reach the core of the Tier Three Spiritual Vein, which only the Lu Family's Golden Core Cultivator can access.
