Epic Nameless Calligraphy / Paintings
Hua Chi and Shu Kuang cannot be recruited with purple tier paintings, unless your intention is to raise the affinity points.
For Hua Chi, you need a very specific Legendary tier painting (Along the River During the Qingming Festival), which is only available from the auction.
You don’t need to give it to him, he will follow you just to have a look at the painting, you still get to keep the painting after inviting him into the party.
For Shu Kuang, he will follow you, as long as Hua Chi is in your party.