The thing is I actually don't know how to do this differently than manually rewriting every mention of "step-mom" or "step-son". And since Michelle's story alone has around 30 000 words and maybe 200 different passages, it would take me probably few hours and there's no assurance I won't miss a word, which could easily break the immersion. But if you know a way how to do this in 15-20 minutes, please share and I will happily do it. Also, it wouldn't make sense to change just Michelle to "mom" and not Kiley and Summer to "sister" as well.
Don't get me wrong, I'm okay with this idea. But I just don't see a way to do it efficiently (maybe that's because my lack of experience)