My Sister's husband and in-laws are trying to stress my sister into divorce

Hello, my sister got married 3 years back and her marriage looks in trouble. She has given her all to the marriage and only got deserted emotionally by her husband. He goes on for weeks without communicating with my sister where as she keeps on trying to get him to speak. Recently he only fights or stays quite the whole time. Her in-laws caused so much stress between the husband wife specially her mother in-law and sister-in-law that within a year and half she had to undergo a brain surgery for too much mental stress. My sister's in-laws have always been hostile to us but we always underplayed it that someday it will change. The husband played no part in resolving this tension between the two families. Recently we got to know that the husband started recording fake notes and fake audio about my sister and my family making false allegations in it, which has us concerned as we never keep record of what happens to us as we had never thought that things would come to this. Please suggest what is going on and furthermore what should we do.