I got upgrades for 3 people Y to J for MEL-SIN and DXB-LHR once (SIN-DXB was EK Y), I was SG, other 2 NBs, so upgrades with more than one passenger do happen. That said I guess it's easier on DXB-LHR as probably half the AU-DXB people get to DXB and then go DXB-Europe, leaving space on DXB-LHR. Harder on the way back I expect.