Goshuushousama Ninomiya-Kun

Gosh?sh?-sama Ninomiya-kun’s story revolves around Shungo Ninomiya, a male high school student trained in difficult hand-to-hand combat. He lives in a huge house with his older sister Ry?ko, who is almost always gone on some dangerous mercenary mission. One day, his sister sends Mayu and Mikihiro Tsukimura, two siblings, to live with him to help Mayu overcome her fear of men. Unfortunately this is accomplished by making Mayu and Shungo share the same room, bathe together and even sleep together in the same bed. Making things even worse, Reika H?j?, the student-council chair, is blackmailed into becoming their maid due to a video that Ryoko recorded, in which she tries to seduce Shungo. ~from Wikipedia
From Baka-Updates:
Shungo is a normal high school student living in a huge house. One day, his sister Ryoko sends Mayu and Mikihiro Tsukimura, two siblings, to live with him to help Mayu overcome her problem. Mayu’s problem: androphobia (fear of men), and Ryoko wants Shungo to help her overcome it. How? By making Mayu and Shungo share the same room, bed, and even take baths together. To make things even worse, Reika Hojo, the student-council chair, somehow ends up becoming their maid.