It will be possible to romance them both. From chapter 10 onward, you'll have a choice to spend alone time with one girl or the other (may not be in all chapters depending on the narrative), which will affect the girl's love points. Depending on how much time you spread between them, you could end the game in a polyamorous relationship.
Planned are J+C end, J+C+N end, and a J+N ending (which will probably require you ignoring Carol at every opportunity), plus some other variations based on the stats you end up with.
As you can see by the image below, you can end Ch9 with both girls in a decent place, so you have a little love to spend.
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Carol isn't exactly into women, but she might warm to the idea of sharing Jack. Maybe a little curious but I wouldn't expect any C+N action. Or at least, not right away.