S.J.
Hi L.,
You don't say if there are children there for your children to play with. If not, they may be trying to punish you for making them go which is not OK. You might try telling them ahead of time that if they use "yucky words" (as we call them at our house), speak to you disrespectfully, or act up, you will be leaving immediately and they have lost ________ priviledge (use of the computer, can't watch a favorite tv show, no dessert, whatever). Tell your friend of your plan ahead of time. Give them the old 1,2,3, then get up and take them out. Your friend will understand.
Another option would be to have your friend say something to them. Talk to her about it in advance. They say that the best way to get kids to listen is not to be their parents. I've done this with a friend's child when she couldn't think of anything else to do. I asked the child if she would talk to her friends like that and told her that her mother was my friend and I didn't appreciate her speaking to my friend that way. I told my nephew that I didn't allow the language he was using in my house. They were both mortified. It also gave their parents the chance to say, "You misbehaved so badly that Ms. S. had to speak to you about it." It gave some reinforcement because then, it wasn't just the parents that were speaking to them about it.
Hope it helps! Good luck!!