Dokidoki Sister Paradise 2

Main character lives alone as his father goes to establish some business abroad. One day father suddenly returns as the richest main the world! He marries a Japanese woman who is 2nd richest person in the world. She has eight adopted children, and if protagonist marries one of them he lays a foundation for world domination. He attends the same school as the new brides in question.

[From vndbreview]