To use your wording:
Critical Phases:
LH Seat: Captain
RH Seat: First Officer
1st Observers: Relief Commander
2nd Observers: Second Officer
During Cruise Phase:
Can be a different mix but most common is
LH Seat: Captain
RH Seat: First Officer
Relief Commander & Second Officer resting.... then
LH Seat: Second Officer
RH Seat: Relief Commander