It's already a given that he is going to fuck the daughters at some point, and possibly even Yuri if this turns into a proper harem (I see usual harems as more than 2 girls, that is just a love triangle where everyone is happy), but I wonder if he's gonna fuck the wife too. Maybe an excuse can be that polygamy is a custom in this world (even though it hasn't been mentioned), and the husband knew there might be a day that comes where his wife sleeps with another man, so he's just wanted to find one that will treat their family as his own.