Does byakuya even like his sister or he is just doing it for his wife?

yes Byakuya likes Rukia. because after his battle with Ichigo it hit him to breck some laws and he
broke his promase to is mother +father to follow the law. when aizen tolled gin, gim to kill rukia byakuya was there and saved her because he proime to his wife Hisana that he would protect he with his life. then had the bravey to tell rukia the truth about why she was put in the Kuchiki family. and tolled her about her older sister Hisana. Hisana don't want rukia to know about her older sister. and what she had to do. leaving her on the steet when she was just a baby. but when Hisana was down to her last bearth, and asked byakuya to adode rukia into the kuchiki family and it was not to be a outsider as they say was not allowed to be in a rolyal family like the Kuchiki family but byakuya did not care because it was for his wife Hisana. so yes Byakuya does like his sister-in-law Rukia Kuchiki (reandom picture of hollow ichigo with Ulquiorra's arm)

He cares about her! He saved her life and loved her as his qwn sister (but Rukia's his wife's sister). He broke his promise because of her and he didn't want her to die (deep in his heart).

just doing it for his wife