Looking for a novel

I read a book one time where the protagonist was transmigrated into the body of the third so of a prime minister. And the opening scene was where he was kidnapped by the disciple of the strongest sect in their kingdom. Then he got an inheritance related to blood.

His father the prime minister wants to destroy all the sects in the kingdom, the royal family feels the power of the prime minister is too much and is threatened by it. His second brother who was seen as the successor to the prime minister was killed by the sects. Leaving him, his eldest brother and his adopted sister.

He was bethroted to the princess of the kingdom who is a general. In one arc, the princess was set up and he, the princess and the barbarian king were all transported to an underground place where he was infected and was in a strange state of immortality but will lose his memory over time. In earlier arcs, he killed the MC and discovered the grandpa who was supporting the MC and the prime minister took the grandpa after he fulfilled the request of protecting him. In the underground carvern, the one who found some sort of cire for that strange immortality state was still alive in a strange state also, and attached herself to him.

There was an arc where his adopted sister created a formation on a city to protect them from a beast tide but a sect wanted to use that formation to let many people died so they can creat some sort of soul resource point. He found out, found his sister and slapped her.