Jiang Cheng never expressed the brotherly love towards Wei Wuxian. His angry nature was an expression of his love. His love for Wei Wuxian was the same as his love for Jin Ling. He had no grudge with Lan Wangji. He just had to be jealous. Jiang Cheng was the most important male in WWX's the world. But after Wei Wuxian met Lan Wangji, Jiang Cheng realized that this was about to change. That's why he didnt like Lan Wangji. But no one could take Jiang Cheng's place in Wei Wuxian's world. Wei Wuxian had special places for each person in his heart. The place in his heart for Jiang Cheng , place for Lan Wangji , place for Lan XiChen , place for Jiang YanLi etc.. No one could change them in any way