Hammond was most likely a bit too traumatized by having his own grandchildren almost killed by Rexy (even if that was accidentally) and by the raptors (which WERE trying to kill them) for him to consider that. And that's not even taking into account him explaining the whole thing to their parents. If he was traumatized by that, then I don't think he can stomach handling the possibility of having other people's grand-kids go through that, no matter how small the possibility is. Not only that, but given how he had to have eventually known what Nedry did, and figured out why in his head, I don't think he could have trusted his nephew either.
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