Hi julesn. I don't have any knowledge of the Sedici specifically but it's very common on modern vehicles to find one engine mount on the "front" of the engine - so the end where the auxilliary drive belt/alternator is - and one on the gearbox end. So one bolted to the O/S inner wing and the other to the N/S inner wing. These mounts take the weight of the engine but need another support to resist Torque - the twisting of the power unit when propelling the vehicle - This support is usually a link from the back end of the engine/gearbox, often from the differential/final drive casing, to the lower part of the bulkhead (roughly where your feet will be inside the car). This link does not take engine weight, it just stops the engine twisting around the actual mounts.
So, as you seem to have found the two weight bearing mounts, you need to have a crawl around underneath - NOT WITH THE CAR JUST SUPPORTED ON A JACK PLEASE - and see if you can spot the "steady" bar. Although most often mounted off the back end of the power unit (power unit being the engine/gearbox unit) I have also seen them on the front, so don't be too surprised if it's there instead!