In-laws instigating end of marriage

Madam- I am asking this question for my sister. She has been married for just about 2 years. She has been having problems with her in-laws. Not only do the in-laws interfere in little things in their life, but in every single decision from her job, what my sister and husband buy for their house to where they go, how they spend money,etc. Her husband completely sides with his parents. Over time, with the instigation of the in-laws he has completely isolated himself from my sister. In all this time, he has not even consummated the marriage in spite of all my sister's efforts towards this. And now the in-laws are threatening (verbally) that he would give her divorce just because she resists listening to every single thing they ask them to do. And he is going along with it. My sister doesn't want to go through with a divorce. We would appreciate advice in this matter. Is there something that can be done legally that would resolve this issue and force better behavior from her husband and in-laws? We would like to know are there any consequences for any of their actions- actions which have made my sister suffer this much in the last two years? Can you please advice?