Dear Izza,
I think you are getting disappointment after facing same behaviour in spite of being good with them. Now listen, Allah says:
"Never lose hope with Allah's Rehmat". Therefore keep trying to rectify their ill behaviour.
Always remember that people in a group fight when they don't have a combined motto.  You had better bring your sisters towards the mission like "be good and spread good" in daily life. Compete in performing good deeds. It will bring a positive change in their lives and in your family as well.