You are the master/mistress of your home. Tell them to take their argument outside.
If they're visiting you, go get their coats and hand them to the couple, saying, "Well, the visit is over, so please take your argument to your own home."
When they argue on your front lawn, you go out and say, "I don't want to hear this, and you're disturbing my neighbors, Here, I've opened your car door, get in and drive."
But you might first sit down with them when they're NOT arguing (individually or as a pair, whichever you judge most effective) and say, "I'm sick of listening to the arguing. When you start, you take it out of my house and out of my lawn. I'm going to send you home if you start up again, so don't be surprised."
Skip the whole counseling thing (or, keep it completely separate from the "I don't want to listen to this" idea). Just focus on "I don't want to be around the unpleasantness, so you are going to have to take it away from me."