I like to think Touka has a HUGE crush on Iroha, and Nemu is on love with Ui. Too bad for both of them that Iroha is Yachiyo's wife while Ui only loves her Onee-chan...
^^ "A whole new type of narcissism"?
Falling in love with your own reflection is literally the story of narcissus
This is the original type of narcissism.
^^ While Ui does love her oneechan Iroha a lot, I don't think it's necessary incestual love like is with the Amane sisters. As for Touka yeah she really loves Iroha, I mean in the past she even calls Iroha onee-sama while Nemu only uses nee-san. Also Touka, Nemu, and Ui are shown to have a very close relationship in the past.