This is amazing. One of the best humor i saw in VN, right next to unfinished Milf in Time. I know most of people will think that CGs could've been better, i thought myself the same at the start too, but right now i think even CGs and models are fine, maybe not ideal, but kinda suited for the story.
The "sister" should look like that, a shy and perverted girls, as it would be hard to justify the plot and the idea that she never saw real dick in reallife. The "aunt" also cant be a bombshell, as she cant have any relationship because of all this weird shit happening in her life. So she's beautiful, but not the one who really do her make up for someone else.
So yes, the models are fit here well. Probably there could be some improvements on light and scenes, but seriously, its not the most important part of the VN, the plot are.