First, you do as Kim C says and say to them individually "Keep it down guys"

If that doesn't work you shout loudly "BE QUIET, THERE'S PEOPLE TRYING TO WORK"

And if that doesn't work you borrow your teenage son's umpteenthousand watt guitar amp and record their antics and play them back at full volume, live.

I had a similar situation once when us draftsmen shared an office with the estimators. They'd let their phones ring on and on and not answer them while we were trying to work. Asking them nicely did nothing. Eventually, I got to shouting loudly "TELEPHONE" every time their phones rang. Management soon sorted them out.