Imohori ~Onii-chan no Funtouki!~

Main character is half-engaged with another university student, but for formal engagement he needs her father's approval. Alas, father went on a business trip for a week. Protagonist wants to take advantage of his fiance at the winter vacations, so he is limited in time. He decides to live this week at their house. But he could not foresee all the seduction attempts from the members of the family...

[From vndbreview]