I think one of the keys here is the difference between his group and his family. Group: Uncle, agent, others (journalists, etc.) vs Family: Mom, wife, kids? uncle, sister. Uncle is in both groups and that's what Kawhi and he will have to solve.
If I were Popovich or Bufford I would talk to Kawhi's mum, uncle's sister. Explain to her the situation and plans, showing you care for her son. Try to build bridges, fix as much as possible. Bring her on board and you almost get Kawhi. She is probably the only person able of making work that Spurs-Leonard-Uncle triangle.