Responses

The MC is the rightful heir to the throne and I think that's what the ML is trying to correct, make the MC King by removing the aunt from the throne by force. But if the truth that the ML didn't kill his dad, and the aunt/current ruler was involved comes out, they won't need to use force. The aunt and brother killed the Mc's dad, aunt wanted the throne and the black haired guy wanted the MC, the sister later found out and helped her brother cover it up.
OMG - the brother and sister are crooked. I think the brother killed the Uke's father, the sister covered for her brother and pinned it on the Uke, made him a slave and gave him medicine to wipe his memory. This is why they don't want his memory coming back, because the Uke will finally tell the truth. They took everything from him, what an evil pair of sibblings.