Just saying that it look honestly rushed and not really detailled.
Of course. And some of the points you raise are quite valid. I'm not too sure I want the developer to dwell on those aspects of the game though. Especially since the odds of the three of them actually surviving as they did are nearly nil. But (in this game), survive they have. A little suspension of disbelief is obviously needed to get them to where they are at the end of the release... as it is in most porn games.
I do not think it odd at all that the girls quickly adapted to living with the MC. He DID save their lives after all, and they are stuck with him as their only parental figure, and completely dependent on him for everything.
Whether they asked about their parents is unknowable, since we aren't given an awful lot of conversations between them about anything. Filling in those blanks, I would assume they did. I would also assume the MC told them that their was nothing to be done about their parents.
During those early years, the MC seems to have treated the girls with loving care. So, I doubt that they would cower in fear in some corner for all those years.
The real sticking point for me is the sudden change in attitude the MC has toward his charges. That does not make a lot of sense.
By the way, the one choice (other than names) in the game illustrates another inconsistency.