Definitely agree that MC needs to have been older than 5 when abducted. It makes the suspension of disbelief impossible. I get it's important he was away for 18 years so that the twins are legal, but just make MC a few years older. Vanessa says she's worried about his grades in school, but at 5 years old, he'd be in preschool, at most, with no grades to worry about. Also, as Spyder pointed out, no 5-year-old would remember their own address. I'd be shocked if I met a 5-year-old that even knew what city they lived in. For the story to remotely work, MC needs to have been at least 8 when he was abducted.
As for the rest of the game, I'd say it's a rather impressive start for a newcomer. The girls are gorgeous, with a good amount of variety(Aunt Laura is best girl). Perhaps a few too many of them so early on, might be too ambitious. The renders are fine for a beginner, I'm sure they'll get better over time. The length was quite good for an initial release, and the story seems interesting, so far. The dialogue definitely needs a good proofreading. Commas are extremely important, and their absence is strongly felt here. Adjusting for the learning curve, I'd give this game a solid 4/5 stars. I'm excited for the next update, and looking forward to seeing the dev's growth and progress as a writer.