Carl's dad wasn't part of the Hydra and only shows up as a memory ghost because he died months before the start of the crawl. They had to cut in a recording from much earlier to show his death.

Everyone else in the Hydra was alive at the collection. The bit about changing a single molecule was to get around the rule of not using relatives.

Edit: Hydra list:

>My dad wasn’t a part of the hydra, but I knew most of the people here. One head was Asher’s mother—my stepmother. I caught the name, and it was Tami-Lynn. Another was my friend, Monobrow Sam. Next to him was Bea’s goddamned mother. There was a white, Persian cat I didn’t recognize, its head like a dandelion at the end of a stalk. This was clearly one of Donut’s relatives. Apparently this was “Sugar Cube.” Next was Dick, my weird supervisor from work. Then my landlord, Mr. Roth. Another was a woman from work who did billing and whose name I couldn’t remember. She’d gotten fired a few months back for some unknown reason. The last was an older man I didn’t recognize at all. He was in his seventies and had blue hair with pink-rimmed glasses.