How would you arrange these mofos?!
The Professor should definitely be at the top; I would never entrust such an old, frail man with holding up so many people. I highly doubt he'd have the strength to withstand the weight of even one person.
Amy seems to be pretty light, so she could possibly go on the second row; however we've seen that she's put up with childhood obesity several times, and I suspect that maybe she's not as light as the show's creators would have us believe. Being ridiculously rich, she may have obtained one of those nifty treatments that reduces body weight by a huge amount, as seen used by April in "Three Hundred Big Boys". This theory is further supported by the fact that she suddenly gained a large amount of weight in "Teenage Mutant Leela's Hurdles" when her age was reduced, even though the tar couldn't possibly make her larger. It likely caused the weight treatment to be nullified somehow. So because of this, I wouldn't risk putting her near the top of the pyramid, just in case she suddenly becomes fat and causes the whole thing to lose balance and collapse. Amy can go right at the bottom.
The two kids, Cubert and Dwight, should probably go on the second row, under the professor. They're only children and might not be confident holding a large number of people up. I'd say they'd likely appreciate the view from near the top, as well. If they get into an argument somehow (as they often do), then there isn't too much at stake since it's only the Professor above them, and I trust that Cubert would treat his father carefully.
Hermes, being a pretty big guy, should be placed at the bottom next to Amy. With all his limbo practice I'd image he'd be quite comfortable being underneath stuff.
Bender is easily the strongest of the group, so he should certainly be at the bottom. The problem is though, I'm not sure how they could convince him to do so. Since he's absolutely convinced that he's superior to everyone, the idea of not being at the top would be a major injustice for him. Perhaps the company could chant "Bender is great! Bender is great!" as the pyramid is assembled, and his blimp-like ego would be satisfied.
Now, for the final person at the bottom, I suggest Dr. Zoidberg. He's pretty strong and it looks like he weighs a fair bit, but the main reason he'd be preferable is because if he was on top of somebody else his claws could easily cause major discomfort, which may potentially lead to disaster.
That leaves Fry, Leela and Scruffy to go on the third row. With the exception of Leela, they all have somewhat neutral strength and weight. To be safe though, I'd position Scruffy between Fry and Leela so they don't distract each other too much during such a delicate operation. And there, we have our pyramid.
...why were we doing this again?