FC, (fielder who grabbed the grounder or caught the pop up) to (Fielder who caught the ball for the out at 2). Then RBI for the hitter. If it's a Sac Fly double play, not sure you award an RBI, but that is probably not going to happen very often.
The more common example would be ground ball, and I'll assume it went to a middle infielder as your fielder did not throw home. Then, it would be FC 4-6 (if grounder to second, who throws to SS at 2), awarding an RBI to the batter.