Thanks for the chapter!
MC has no sense of danger if she's enjoying the accommodations more so than at the academy or home despite being kidnapped. Reason Lana is shaking is because desperately trying to suppress her laughter. Unfortunately for the MC Lana has taken a very big liking and interest in her. Although not really shown there are other servants there, it's just a minimum staff for security (basically only have a few servants whose loyalty are sure of to decrease chances of one of them leaking what they're doing to anybody.) Serina is depressed because feeling guilty over kidnapping MC and under misconception that MC is putting up a brave front rather than being honest. That butler is definitely a Dark Magic user. Serina went from emotional and about to talk to quiet and docile along with that black cloud hanging around him when he whammied her. As for Serina being the one who planned the kidnapping I highly doubt it with Rufus' Dark Magic. Betcha dollars to doughnuts he probably guided her to the idea with the hope that doing so would help her husband become the heir to the throne while using Dark Magic to push her to go with it, not think or doubt about doing it, and probably a bunch of other things for his boss. Doubt his boss is one of the other princes, but likely a high ranked supporter of one of the others who will be more likely to get the throne as Gerard will have signed his rights away and Serina's husband will be too guilt ridden or smeared by what she her kidnapping MC to have any chances. Boss likely a noble wanting more power so was able to arrange a nice place and luxury items for MC's stay, but not so high ranked that has a lot of loyal followers or there'd be more guards and staff to help keep MC in captivity. Then again could be limiting it to just Rufus, who is talented enough to escape on his own, and a few sacrificial individuals who obey and believe Serina is in charge. That way after Gerard signs away his right to the throne she'll take the fall suspending any further investigations into the matter. Although this is just me guessing, author could pull out some trick or something so answers are completely different.