Flight crew scheduling for long flights

Anybody who monitors this are of discussion knows that I post lots of questions and many relate to QF A380 operations, but I suspect the question I have relates to other airlines and routes as well.
SYD or MEL to DXB is about a 14 hour haul and is crewed with a total of 4 pilots under normal (non check ride) circumstances.
The onward flight to LHR is approx 8 hours.
I am not sure if the requirement for a relief pilot starts at 8 hours or where but if the relief pilot is required that would be 3 pilots and not 4 required.
I am interested to know if all 4 pilots would go on to LHR (after the required break. I assume they would take the flight on 24 hours later) or if they go on with the required 2 or 3 and the remaining pilots are scheduled to fly back to SYD or MEL or on to LHR on different flight.
These are the riveting questions that you come up with when you are retired and want to keep your mind active.
Any insight would be appreciated

Good and important question! Affects morale as well as safety!

I don’t think any of the pilots would be flying the aircraft on to LHR. Their duty day would be over and they would require probably 24 hours of down time. I’m retired over 12 years, myself and these torturous duty days is the main reason I got into the A-300’s and flew mainly between MEM and CLT four and a half days a week! Left MEM around 4 PM, went to the hotel, left CLT about 7 AM! Sun always at your back! Worst part of these L-O-N-G, intercontinental flights was seeing the Sun come up… especially in your face! LOL! Perhaps going west would be better? Either way, your internal body clock (circadian rhythm) is screwed up!