All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
First of all, it should be mentioned that the parents have no right to oblige their son to marry a girl whom he does not like because such a conduct may lead to unpleasant consequences on the son and on his family. Also, the son is not obligated to obey them in this regard and he is not sinful if he does not act according to what they say because obedience is required only in what is permissible and it is not within what is permissible to oblige the son to marry someone whom he does not like. For more benefit on the limits of obedience to parents, please refer to Fatwa 86982.
On the other hand, divorce is permissible but we do not advise you to hasten to it as Allaah urged us not to hasten to divorce even in case of hatred between spouses and He highlighted to us the good outcome of not hastening to divorce saying (what means): {For if you dislike them — perhaps you dislike a thing and Allaah makes therein much good.}[Quran 4:19]
Moreover, it is confirmed that the Prophet said: “A believing man should not hate a believing woman (i.e. his wife). If he hates one of her characters, he will be pleased with another.” [Muslim] Additionally, not all homes are built on love as ‘Umar said. For more benefit, please refer to Fatwa 86796.
If we presume that the wife reached the state of recalcitrance, then there are some steps in the Sharee’ah regarding how to treat a recalcitrant wife and this is clarified in Fatwa 85402.
Therefore, we advise you to be patient as much as you can and endeavor to rectify your wife. However, if the marital relationship with her has worsened and there is no other alternative than divorce, then it is permissible for you to divorce her even if your parents do not agree to it, and you are not sinful if they become angry with you due to this. As regards your sister being divorced by her husband, then this may not happen at all, and if it happens, you are not sinful for it as well.
Allaah Knows best.