My only question about this is, will she have her own girls or will she be chasing the same girls as the MC? if it's the second then the NTR you didn't plan for is already planned.
I'm not saying that's the case here, but I want to know why many think NTR can only be when there's a dick inside the LI. Being betrayed/exchanged by a woman is also NTR.
Edit: I see the facepalm has started, so I want to make it clear, I have no problem with lesbians. I'm just wondering if we're going to share the LI with the sister.
If she's gonna get her own girls, that's cool. I have not played yet, just read the comments about the sister being lesbian, and would like to know that. Since the DEV said he won't have NTR, but if his sister is going to "steal" LI from MC, that's NTR, no matter the gender of who is stealing. However, the DEV may consider that it is not. So that's it, it's a simple doubt. No sexist discrimination here.