My Three Sisters Are Transmigrators

The only son of the duke, Liviere, realizes his three sisters have changed one day. While checking on them, he overhears their “secret convention meeting,” where they discuss their previous lives and the time when they were all best friends. He can't make head or tail of anything they say as their shenanigans start to cause him headaches and troubles.

From the same world as The Wicked Gamble and The Grave You Made (BL).