Does a wife's participation with her husband in watching foreign films that contain violence and fighting make her sinful, or is it better for her and her daughters to leave him?

Films are not forbidden merely because they contain violence. However, if they contain forbidden elements such as women and music, then watching them is forbidden. For everything that is forbidden in itself, looking at it and watching it is forbidden, because it is an aid to disobedience or a رضاً (acquiescence) to it. It is not permissible for a Muslim to be present in a place where there is evil unless it is to change it. Otherwise, he shares the sin with the one who commits it, based on the Almighty's saying: "And when you see those who engage in [offensive] discourse concerning Our verses, then turn away from them until they enter into another conversation."