To achieve different endings, players must adjust their in-game behavior. Endings are not achieved through dialogue options, but via three different mechanics.
Esther never uses the night essence. He stays at Kalyks side and returns to the hunters order.
Path A leads to:
Ending 1
(N0,E0/1,K0) Esther comes back to the hunters order.. None of his problems have been solved. Only if he follows the strict rules of the Order will he be taken back.
Ending 2
(N0->1,E0/1,K0) Esther uses the night essence after coming back to the Order. He is imprisoned. He can either fight his way free, or escape and defeat the final beast anyway as proof. He leaves the Order again, leaving his old life behind, as well as Kalyk.
Esther uses the night essence, but is not completely overtaken by the hunger. He does not follow Kalyk to the order. Their cooperation exacerbates their problems, and the brothers argue constantly.
Path B leads to:
Ending 3
(N1,E0,K0) Esther and Kalyk part ways after defeating the final beast. As proof that Kalyk killed him, Esther cuts off one of his arms and gives it to his brother. Esther walks free, and Kalyk goes back to the Order.
Ending 4
(N1,E1,K0) After collecting all the mementos, Esther realizes it was the hunters order that drove them apart. He convinces Kalyk not to return to the Order, and they promise to be better to each other. Esther stops using the essence, and Kalyk supports his brother. The two flee the country.
Esther succumbs to the hunger and becomes a monster. He destroys everything in his path, including Kalyk and the Order.
Path C leads to:
Ending 5
(N0/1,E0/1,K1) Esther no longer understands dialogue. Visually, everything is chaotic and distorted. There is only destruction. Esther is alone, as a depraved beast.