Well I would hold up a bit....
So you added the rock and sand at the time you set up the tank?
Did you see any ammonia at all? Do you have any nitrates?
Because with that much LR, and no additional ammonia source, you may have somewhat of an established system. It may be able to handle the fish.
Now, as I see it, you have two options:
1) return the fish, then "push" the tank with some dead shrimp from the grocery. You may see ammonia, you may not....but you know you have challenged the biological filter. If you do get ammonia, the tank will cycle.
2) Keep the fish, but be slow to add more and watch your feeding. You may be OK, and just need to be careful in overburdening the filter by adding lots of fish. Watch your water quality to see if you get ammonia now that you have an ammonia source (they are effectively like what the dead shrimp are in the scenario above). You may not see any more ammonia...then just be slow in stocking. You may see ammonia and then take the fish back for "holding" until the cycle is completed.
But, IMO, you are not guaranteed at this point to see an ammonia spike with the 2 small fish and 30lbs of rock.
Biowheels are not really "bad" just potentially not necessary. IMO not with all your sand and rock, but the concern is that the pads will trap food and this will basically rot there...so rinse the pads often. The wheels are sometimes called a "nitrate factory" but this is misleading, IMO. Just that they are very effective at breaking down ammonia. I think read up some more on that, wait and see how your tank does, and then make a decision...if you end up with a lot of nitrates, you may wish to remove them and just use the filters for circulation.
