If I remember right, in the censored version it's "step-sisters" and "step-mother" instead but since Patreon went all in against incest, it could be even more censored already.
This game is worth it by the space setting alone (not that it's the only good thing, just that it's enough reason to be played) if you are into space, enjoying incest isn't required by any means even if it's one of the main points. If you don't consider "step" as incest you could play like that with no problems.
You could even play the uncensored version and not romancing your family members if you wouldn't be into that, like you would in real life. There are many other LIs that aren't family.
I'm not heavily into incest but here it's presented in a way that's neither too overboard nor creepy, it's well blended with the drama and the family secrets of the past.