I've just read chapter 1.
Basically it begins with main girl, who is his class rep, asking if she can live in with him. The main lead replied that it would be a problem as there're already alot of occupants. The 3 other girls are not his sisters, but his classmates who (
because of various reasons) have to live in his house. For some reason his parents don't seem to mind having them around.
This is the mangaka's website:
http://yui.sakura.ne.jp/