The 77 designation means the tire is rated for a maximum load of 908 pounds at recommended pressure. I'm not certain of the unloaded weight of the bike, but I would take the unloaded weight (meaning, no riders), and divide it by two, then add the weight of the passengers.
So, let's say the bike weighs 750-pounds without riders. That's 375-pounds per tire in load. Then lets say one rider is 200 pounds and another is 150 pounds, for a total of 400 pounds. Finally, factor in the weight of gear (jackets, helmets, luggage, clothes, etc), and let's say that's another 20 pounds. The combined total load on the rear would then be: 375+200+150+20, or 745 pounds, so you should be within the safe range.
I wouldn't recommend you ride "at" the maximum load rating, so if real world numbers are higher than the example from above, you'll want to give it careful thought.
10 months ago