How would I discuss the situation with the girls without criticizing their mother? How do I tell them that they should not be treated like this so that they have some self esteem? Or do I just let the girls stay at my house and say nothing?
I think the best thing you can do is just tell them they are always welcome to stay with you, just as you already have. If it becomes a regular occurrence, they'll trust you and you can then have a conversation about how they feel about it and you can do some supportive listening rather than criticizing your cousin. Since the girls confided in your kids first, make sure they also know you want the girls to feel welcome whenever they need to stay overnight. Keep it light? Teens are sponges. They know that actions speak louder than words and they will see you are a safe place both physically and emotionally. They're lucky to have you