I don't know. I'd have to see the actual numbers on that. You consider only women can get pregnant (whatever percentage of the population they are) and not every woman is pregnant all the time.
But yeah, there are people that do have at least two skeletons in them. If you then consider twins and triplets, dear heavens!
And I suppose there are the animals we swallow. But during the normal course of eating, we don't eat the bones. And accidental eating (I swallowed a bug), bugs are exoskeletal, so I'm not sure if those types of things would count.
And now in the fourth paragraph I'm considering that maybe I'm looking far more into this than I was meant to.