What type of surface is the landing?
If it's a hard surface, get a bath mat or hall rug that is soft on one side and has that rubbery anti slip texture on the other. Set it upside down on the landing and land the tank vertically on it. Then, VERY GENTLY pull the rug to get the tank sliding slowly over the edge until you have enough exposed to put the suction cups back on it.
Two people each end, one per suction handle. The longer armed people should be on the lower end and the ones with stronger backs up top. Don't be afraid to keep it very close to the stairs and set it down on them every step. If the stairs are crappy and you have some 2x4s you can lay down as tracks, you can slide the tank right down the tracks to the landing, re-orient as noted above, and do the same thing again.