Responses
http://www.mangago.me/read-manga/step_siblings/
http://www.mangago.me/read-manga/kedamono_kareshi/
These are some manga for the different pairings from the game of Brothers Conflict where she gets lots of step brothers:
http://www.mangago.me/read-manga/brothers_conflict_feat_tsubaki_azusa/
http://www.mangago.me/read-manga/brothers_conflict_feat_natsume/
Any mangas where a girl goes to a new house with one parent and slowly falls in love with her step brother