
After getting 600+ chapters far in the novel, I have developed images of the characters in my head and so far only Anna fits that lol

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.

Can someone explain why the kids can't bring store bought food to school? Like I'd understand if it was already open or something because that prevents a hazard, but why won't they let children bring sealed store bought food?

I’m no expert on Japanese culture and this is mainly based on other manga I’ve read + googling but I imagine it’s mainly just the high standards of Japan have nutrition. Convenience food, while healthy in a way, still contains food preservatives and stuff and apparently they take children’s lunches really seriously (pretty much to an artistic level) and not following through would mean you don’t care enough for your child’s health and upbringing. In further detail, the artistic value of the lunches allows the children to overcome their pickiness of certain foods and have a habit of enjoying them as they grow up.
Of course it’s kinda one of the common nonsensical rules about Japan that (while has good intentions) is almost based entirely on the way the public views you, like how salarymen go home super late at night just to show they work hard while ignoring the quality of work.
Other reasons for the bento box situation the kindergarten’s many incentives to force the mother to challenge ‘motherly’ activities (this might also be related to low marriage/birth rates). They might also be more worried about drawbacks like parental and child complaints e.g. a child starts to complain that they want convenience store food or their mother doesn’t care enough to cook for them when they see other kids with homemade lunches. Also, while a bit of a stretch, it could also be a food package waste reason. Anyway from my understanding those are all the reasons I can think of but I’d enjoy seeing other people’s ideas.

Spain. Well, I said that taking into account my experience, in another place in the same country may be is different. I've been in a "State-controlled school" (I look up linguee, how it's said in English) and children from 2-3 to 15-16years old eat there, obviously parents pay for the meal but it's the school who is in charge of cooking. Some of my classmates had their meal made at home but they also eat in the school (there are fridges and microwaves in the dining room) and a very few people went at home to have lunch. (sorry for my mistakes :'v, I tried to do my best writing in English)
Looks like the novel hasn't updated since December 2018.
https://www.novelupdates.com/series/i-am-a-princess-responsible-for-settling-circumstances/
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