Join the club! I really think Steinberg could usefully provide much more clear information about using more than one UR824 together.
You don’t need to use wordclock with two 824s, you need two ADAT cables. If you look through the threads here, you’ll see that this makes one unit your ‘master’ and one your ‘slave’. You’ll need to set your slave unit to ADAT on the front panel.
What caused me grief was the fact that you need to prepare your slave unit BEFORE you connect it via ADAT to your master. You do this by using the DSP Mix software, not Cubase. You need to route the inputs to ADAT outputs and then save the settings. There are threads here that explain that.
Good luck; once set up they work superbly.