https://www.novelupdatesforum.com/threads/%EC%95%85%EC%9D%B8-%EB%82%A8%ED%8E%B8-wicked-husband.175787/
It's the novelupdates one, I am so sorry for being late >.<
Hi! This is the spoiler forum I've read, it's only 3 pages but I believe it already has the whole plot spoilers.
https://www.novelupdatesforum.com/threads/%EC%95%85%EC%9D%B8-%EB%82%A8%ED%8E%B8-wicked-husband.175787/
Now, to answer ur questions, I haven't read much abt the guards but it suggests that they are genuine with FL. As for the king, hehe, he's evil, I think he's actually the main antagonist and the perpetrator why FL died in 1st TL. FL doesn't remember her 1st life but the ML does because he's the one who made it happen. However, in order to do that, he had to kill FL for 7 times that's he remarks how FL is fragile and also why he's overprotective of her. There are lots more details to read in the forum so have fun reading it!

SPOILER
Okay so basically up til now, it’s clear that the Duke must have reincarnated so it’s highly likely in the other timeline, she was executed for researching opium. After reincarnating, Cesare is taking NO CHANCES so he’s choosing to eliminate all obstacles. It’s not bad but Jesus the way they coddle her is so intense.