Here are a few group game ideas that would be great for joint or combined ym/yw activities...
These ideas are all from ldssplash.com
"Frisbee Swat - What you'll need for this active game are two (or more) Frisbees, two chairs, two cones (or liter bottles), two teams, and a rolled up newspaper for each player. At each end of the playing area, place a chair with a cone on its seat. The purpose is for each team to knock the other team's cone off the chair with a Frisbee. Points are awarded for each knockdown. Team members pass the Frisbees to each other as they work their way down the field. No one is allowed to run with the Frisbee—they can only pass it. Team members hold a newspaper in one hand, which is used for knocking down the opponent's Frisbee, and use the other hand to catch and throw their team's Frisbee. To play the game teams must attempt to score on offense and at the same time maneuver around on defense to swat the opponent's Frisbee out of the air.
Faith Factor - (based on the idea of Fear Factor) with the YM and YW we had competitions such as who could get the most gummy worms out of a bunch of chocolate pudding using only their teeth; who could state the years theme ("Let virtue garnish thy thoughts unceasingly...") with the most marshmallows in their mouths; bubble gum blowing contest, etc. It was a lot of fun--not totally a spiritual activity, but a lot of fun.
Blind Volleyball - Set up the volleyball net and drape sheets over it (safety pinning them in place). Then you just play a normal game of volleyball, you just can't see what's going on on the other side of the net! We played with a giant ball that was soft"