Yeah you will need to switch out your Dodge Grand Caravan factory roof rack with another system. I recommend going with the Thule 430 Tracker II roof rack system. It attaches directly to your Dodge Grand Caravan factory rack tracks, replacing your current incompatible factory rack which will not allow you to connect a tandem bike rack or other gear carriers to the factory bars, nor is the factory rack rated to handle the weight. The Thule 430 Tracker II includes a pair of load bars, four 430 Tracker II feet and a set of four TK Tracker Kits (choose the TK1 Kits for your configuration) that snap directly into your roof tracks. You can then attach the tandem bike rack and other bike carriers directly to the load bars. The 50inch load bars are the recommended length for your vehicle's roof top.
The
RockyMounts R4 tandem bike rack is your best bet. It is more affordable than the Thule tandem bike rack option and it performs as well if not better. It mounts directly to the Thule 430 Tracker II base rack load bars.
Rocky Mounts also makes a very reliable fork mount bike rack called the
RockyMounts Lariat SL bike rack that is considerably less expensive than Thule bike rack options and attaches directly to the Thule 430 Tracker II base rack load bars too. Even have the choice of multiple color options. You will need to order a separate Rocky Mount lock to secure each bike to the Lariat SL bike carrier (will not work with Thule Locks).