First few chapters in and..

PFFFFT HAHAHAHA NO

I gotta know, what gave you this idea? She's the most loyal out of all the witches to the point where she is overzealous which is why it's shown that Anna would make a better Queen than her despite both loving Roland

Totally agree. The most shocking one for me was Roland
I was so confused with his hair and how different he was from my imagination

No, if anything this handles the whole concept of a "harem" very well. I wouldn't even call this a harem.

There is a spoiler below. I will notify you by putting a warning in all caps before saying it.

Roland is very adamant about loving only Anna and being loved by her in return. Even when Nightingale is jealous it's more of a sad jealousy and not an angry, I'm going to hurt someone or myself, jealousy. Regardless tho, (AND THIS BIT IS A SPOILER IF YOU DONT WANNA READ ON) she not only becomes is best friend and closest confidant, but essentially also becomes his top bodyguard/shadowguard (which she's already showing signs of now), the chief of investigations in the new capital and eventually the kingdom, and eventually with Anna's acceptance/permission, Roland's second lover. The author makes clear distinctions between Anna and her qualities as a queen and Nightingale and her qualities as a shadowguard/zealous devotion to Roland. There is even a time when Roland is injured so Nightingale, one of their strongest fighters just freezes. It is up to Anna to take control and save the day despite Nightingale's higher experience since Roland cannot give commands. Nightingale loves both Anna and Roland very much. Their society also is used to nobles, especially monarchs, taking multiple lovers, the previous king Roland's father being and exception, only loving his wife. People bat an eye more at Roland taking not one, but two witches who cannot give him an heir since witches are barren, than only having two lovers.