Responses
http://www.mangago.me/read-manga/ganjigarame/ (oneshot)
http://www.mangago.me/read-manga/nanadome_no_gomenne/ (tragedy oneshot)
http://www.mangago.me/read-manga/ai_to_makoto_moriyo/ (polyamory + twincest)
hope that helps (●'◡'●)ノ
Anyone know of any Twincest stories? xD