Imo in comparsion to all characters that we currently met Nefail is the best(big sis, a bit tsundere and protective, will move mountains for Elifael, in comparsion to the middle sister that all sweet on the outside while being the opposite in the inside, Nefail on the other hand is all hard but actually big softie), Maryl is second best for sure(human servant that is in love with her master, classic), they are developed the most, but even if they werent Nefail is just the type of character i always liked in all kinds of media, middle sister is obviously has more to her than we saw so far, she seems like a wolf in sheep clothes to me with her "sweet" attitude wich is fine but i prefer the other sister, characters like that gnome girl hardly count to be honest, her scenes are nice but she is obviously a side character wich is fine, Sally i really like but she is not really a "love" interest(but i still prefer her to make apperances in the story, she is really nice addition, the fact she is not attracted to regular girls limits her involvment tho but that fine).
I liked the mother but to be honest, she does not feel like any other person in the story(she is like some kind of demigod in comparsion to others wich is fitting), her scene was weird and fun and she is kind of creepy in a good way, more scenes with her would be cool, but i dont see them happening for a long time.
Main character is awesome that for sure, she has a great adaptable personality and a nice sense of humor, stuff like that is rare in MC to be honest wich is great for a text based story.
You said to pick up to 2, but even tho i like Maryl as a second best, the gap between her and Nefail for me is too great, big sis all the way.