You do realise this is a sex game, right? And that it has clear incest elements too? So there is absolutely no way that the purity path will not lead to being just a loving father who does nothing sexual with his daughters or ends up single at the end. Purity likely means that you'll treat your daughters as well as other women with respect and dignity, getting them to like and fall in love with you because you present yourself as a kind, loving, and considerate person. This path is also referred to as Romance which clearly indicates that there will be romantic involvement with one or more females characters, and the daughters will certainly be among that.
As for the other two paths, Lust seems like it will be one where you'll just have no strings attached sex that doesn't cross over into romantic feelings, like if a female character were to ask a question like, "Is this just sex or something more?", the MC's response on a Lust path would likely be, "Just sex." The Darkness path is probably going to be the all-out depraved route, where the MC treats women harshly, forcing them to submit to his will and making them his sex slaves. I personally don't like this path or even having it as an option in the game as I feel it doesn't fit with the MC and the tone of this game, but I guess there are some people that get off on this.
Interesting to note though that the recent poll on Patreon asking people which path they will take has Purity in the lead followed closely by Lust and Darkness is way, way below both of them. It only has 167 votes at this time (around 15 of which have voted for Darkness), but it's interesting to see the current lack of interest in the Darkness path.