Replying to Synthetic marijuana

I live in a house that my family owns with my little brother and he has 3 friends that are currently staying with us for free (one even has his trashy gf staying here with him), they sleep on my couches and they eat all the food and drink my beer. Lately they have started smoking synthetic marijuana like crazy and are always passed out all over my house. I found one of the guys girlfriends on the ground in the garage and thought she was dead at first. They get so messed up that they can't even talk. I'm completely sick of it and so is my brother but he won't tell them to leave. He keeps telling me that they are about to move out but it has been two months and they are still here. What should I do? I really don't want somebody dying in my house...