I want you to note that God's instruction to Ezekiel was that he was to shave his head and beard and then it was to be precisely divided. It was not just a matter of, "well divide it into three piles." No, He told Ezekiel to use balances and I think what He wanted here (since no other information is given) is for each of the piles to weigh exactly the same amount. So we have a very precise division or separation of the hairs of his head, which of course you understand represent the population of the nations of Israel.
Now I think the "them" from the context has to be the last of the third, those that he is to scatter in the wind. So we have one pile here, one pile here, another pile here. That third pile he takes and throws it. However before he does it, he just takes a small number of that pile and holds it back and he puts it into the folds of his garment, or (as we might say) into his pocket. Then what remains, he throws up into the air and it just gets blown away. Now we understand this of course means that it represents those people being blown into all nations, being scattered in captivity.
