It's difficult to just happen into a dvp. It does require all participants to be on the same page. It's good to be aware that getting into the position does require a decent sense of humor.
So, since she is concerned about enough room, be very careful. You should be the top guy. Get the bottom guy in as deep as possible and allow her time to adjust to him. The position is bottom guy with legs together, her cowgirl, chest to chest, you are coming in doggie with your legs between hers and his. Getting your dick in should be done pretty slowly and with too much lube. Once you get the head in, let her adjust again and don't push until you feel her start to push back, or tell you to give her some more. Once you are in, you will still probably have to go pretty slowly but let her set the pace. Keeping everyone somewhere between soft and shooting is tricky but with commitment and practice, you too can soon be DVP masters.