I am trying to piece together a DONE4, ex-JNB. A red inverted triangle flag occurred when I try to transit (less than 24 hours connection) LHR the second time, on way to complete the last flight to JBN.
Here was my preliminary itinerary that did not pass validation online.

JNB-xLHR-xLAX-SCL-LIM-GRU-GRU-EZE-xJFK-xLAX-SYD-PER-HKG-NRT-DEL-xNRT-SIN-xLHR-JNB

NOTES:
x : < 24 hour transit
xJFK-xLAX-SYD is under 1 flight #, namely QF108
xLHR: this leg has a red flag. Therefore can’t validate the itinerary.

Questions:

1. What I have above is a DONE4?
2. Is this (xJFK-xLAX-SYD) allowed?
3. Is xLHR-xLAX-SCL allowed? I recall some Fters had done something similar, by quoting certain rule (which I forgot now).
4. Can someone PM me with contact info of a TA in JNB?
5. First flight is AA codeshare (BA metal), second flight is on AA metal. Can this be ticketed by AA?
6. How can I get this DOEN4 to work?

All suggestions welcome. Thanks.