
From some spoilers I read:
Duke : he couldn't make anyone pregnant hence both women(duke wife and FL mother)had affairs and the sisters were born.Duke knew but he values his reputation too much
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Step-Sister : She tries to harm/blame FL, a gem for emperor or something (I forgot) but was caught and put to jail. FL visits her and tell her that their father never cared for them coz they were girls, he only cared for his nephews. Step-sister breaks Down she was to be send to a monastery with strict dictatorship. She kills herself
.
ML aunt : she's the one who killed ml mother and had his father bedridden in that accident, She wanted to be the in charge of the whole house but when FL came it changed
.
ML : when he knew the truth that it wasn't FL family but his aunt who made that accident happen, he started to change. He love FL after clearing that misunderstanding. But he regrets treating FL that was and saying that he doesn't want Any heirs produce from a member of her family
.
FL : after coming to Marquis estate she wasn't treated well(not as bad as her family) but she knew this would happen so she fake cries fake smile etc. When she realized that they were in huge Debt she started to improve their condition and now they no loner are in debt. She eventually confessed the truth to ML that she didn't love him and did that to escape from duke. But after ML confess she started to like him slowly
.
Ji-Ho : He did BETRAY FL in 1st timeline.but after fl died he realized he loved her(to the point of obsession) so he turns back time and let fl have her memories coz he feel bad for her. He so in love(obsessed) with FL that he will do anything for FL if he thinks it's good for her he doesn't care if FL likes it or not he even kidnapped her once. He dies in end tho
.
Servants of Marquis estate : They all fell in love with FL she she solved the debt and gave everyone salary and improved living.They started to feel pity for her coz ML didn't love her BUT they even started blaming ML for ignoring and not loving her(lol)they rather want FL then MLthey are all just cuties
.
Ending : FL and ML remarries to Start a fresh coz their first wedding was when they weren't in love or knew each other well. They have Twins. FL is strict parent AND ML is soft one
(Maybe I missed a lot parts but key spoilers might be this)
Drop any more added spoilers in comment if you want :)

We know Jaekyung paid Dan dept and all but that doesn't make him his possession....and definitely don't deserve to be treated like a toy... :( Dan might be having feelings but just imagine if Dan paid all the dept money back he got from Jaekyung and then leaves being his personal doctor. Jaekyung I hope he redeem himself somehow....but I really wanna see him suffer how he made Kim Dan suffer so much just coz of his "Jinx"
Is there Amy spoiler for this?when I saw Ch.1 I thought it was the guy who was reading the letter in oldage
Uhm... yeah, i thought so too..like you can't tell if it's an old woman or an old man just from their back. The letter too... it's undoubtedly written by satoko..but why would she cry reading her own letter?? It's strange...
True, and when I zoomed in I think I saw Adams apple so it might be the guy