Soliciting Advice PLEASE!!!!

Well, the kids came home late Friday night safe and sound (thank goodness). However, they both came home taking the Lord's name in vain. I am so frustrated. I am so tired of having to undo all of the damage that gets done every time I have to send them to Sandra. And I am afraid I did not respond very well to the situation. With Jaysen, as he was the first one to curse within minutes of being home, I gave him a calm warning (that Alex heard) and told him that it was unacceptable to use that kind of language in our home and that I did not want to hear it again. I let him know that if I heard him swear at all again he would get his mouth washed out with soap and he will be grounded for a full day for each swear word he uses. Fast forward to this morning and Alex tripped and fell and out comes the same cursing. This time I responded with ANGER. I yelled and screamed at her and then proceeded to give her the same speech I had given Jaysen only in a much harsher tone. Then we all piled in the car and went to church. Not the best way to start out your Sunday morning. I could really use some advice on what to do. How do I combat such a toxic and unhealthy environment. They are exposed to so much garbage and filth while they are with Sandra and then I spend 6 to 8 weeks undoing everything and re-teaching things. I don't know how much longer I can keep up this cycle. I know I am not being very Christlike toward her and I am working on it, but in the meantime, any suggestions would be greatly appreciated.