Haven't done it myself but on a fleet where some of my colleagues have - UK>China>UK.
The in house forum where this was being discussed between those who had done it recently/were about to do one of these is locked down ATM
but as I recall the discussions:
Typically 7 pilots in total.
Leg outbound from UK run as a standard 3 pilot sector (2 operating, third as the "heavy"/relief) with the other 4 pilots resting in the cabin or crew rest area.
Turnaround..
Leg inbound to UK run as a 4 pilot sector (2 operating, 2 "heavy") with the original 3 pilots off, resting...
As I recall the discussion before it got locked down there was some debate about how to handle the shifts on the 4 pilot
inbound sector - whether to just schedule the rests in our standard way: the Operating crew in the seats up to almost half way, then heavies in the seats for a long shift, then switch back Op crew in for the last hour, or go for more frequent changeovers/shorter "shifts".
Oh, and hotel available at base...
HTH for now, at least until somebody pops along who has actually done one of these.