Go to your garage and get in the vehicle you want to duplicate, have friend get in the passenger seat, go to phone, Internet, dynasty 8 real estate, and find an apartment in the same building you have,(works best with 10 car garage), click buy apartment and it should come up with black screen asking if you want to confirm your purchase and you click A to confirm and directly after you confirm spam B like 10 times. Should spawn you out of garage and your friend will have to drive out. They then take that car to there garage and park it near the garage door, then they get out of the car and walk inside there garage, they then take any vehicle out of there garage and drive out, when they get out there vehicle they parked outside will disappear and they drive back into there garage and the car you want to duplicate will be in there garage, reminder, the car you dupe from your garage will replace the one in the same spot as there garage. Hope this helps, otherwise look it up on youtube