There's another prominent game about a step brother and sister, and they have an active Patreon.
Patreon's checks aren't perfect. A lot of people do a lot of shit there for a long while before being kicked. And they let people off for absolute BS excuses. "It's not your mom it's your landlady." "The kid may look 12 but it clearly says he's 18."
DPC would likely get away with it, but as a whole the game reads as non-incest.
Tommy specifically seems to actually see Josy as his sister. Josy is quick to correct people and say that they are step-siblings, but Tommy always leaves the "step" out. According to Pete Josy's step-mother Monica was very worried about her. He could of course just be straight up lying about it or trying to convince himself, but then Josy could be twisting things too.
Mostly I see the characters' last names as trivial details, but Tommy's might actually be significant. If his last name has been legally changed to "Taylor", it might mean he actually likes his step-dad and step-sis or at least supports his mother's happiness. He is just a bit tsundere about it.
Mere speculation obviously, but Josy's backstory has gotten way too little attention, so I kind of expect there to be some twist to it. That or Monica turns out to be insanely hot.