Unsure if 72hrs TWOV available to us

We are heading home from USA to Australia (& returning to USA in Jan19). We want to transit through Kunming where we have relatives and a 72hr TWOV would be ideal. Unfortunately the only flights from USA to Kunming stop at either Beijing or Shanghai.
1. After changing planes at (say) Shanghai to go to Kunming can I obtain a TWOV?
2. I may be forced to purchase our flights as two seperate tickets. (ie LAX - KMG then KMG to Cairns, Aust). Will this enable me to get a TWOV?
Thank you