So the Warui series has like 4 couples. u can read them in that order which u listed. If u do read it in that order, u can see characters(that later have their own stories) being introduced and showing up in the story. Or u can read it in the 4 couples's order (Copied from the comments):
Mikado x Towa
First Book: Warui Koto Shitai
Second Book: Warui ko demo ii?
Third Book: Warui Yatsu Demo Ii
Fourth Book: Warui Koibito ja Dame?
Fifth Book: Warui Ouji Demo Suki
Shinonome x Yukimura
Sixth Book: Kirai Ja Nai Kedo
Seventh Book: Koi Ja Nai Kedo
Eighth Book: Kare Ja Nai Kedo
Ninth Book: Sunao Ja Nai Kedo
Tenth Book: Himitsu Ja nai kedo
Extra: Warui Koto Bakkashite Gomennasai
Aikawa x Nanao
Eleventh Book: Mujihi Na Otoko
Twelfth Book: Mujihi Na Anata
Thirteenth Book: Mujihi Na Karada
Kousaka x Akagi
Fourteenth Book: Shouwaru Ookami ga Koi wo Shita Rashii
It says its a series but im a little confused to all of these stories go together or can I read them in whatever order or does it have to be this order plz help me on this and if they aren't all connected with ones are connected and which ones aren't
Vol 1 Warui Koto Shitai [1-1]
Vol 2 Waruiko Demo Ii? [1-2]
Vol 3 Kirai ja nai Kedo [2-1]
Vol 4 Koi Ja nai Kedo [2-2]
--- Warui Koto Bakkashite Gomennasai [1-3 & 2-3]
Vol 5 Warui Yatsu Demo Ii [1-4]
Vol 6 Mujihi na Otoko [3-1]
Vol 7 Warui Koibito ja Dame? [1-5]
Vol 8 Kare ja nai kedo [2-4]
--- Warui ko Tachi no Bansan [1-6 & 2-5]
Vol 9 Mujihi na Anata [3-2]
Vol 10 Sunao ja nai Kedo [2-6]
Vol 11 Mujihi na Karada [3-3]
Vol 12 Warui Ouji Demo Suki [1-7]