Can these locks be rekeyed to the same key?
With that last bit of info, there is no way to key the Norwalk alike with the Schlage using the existing tumbler, it must be replaced with a Schlage or even Baldwin tumbler, which has a Schlage keyway. Yes you can still do it yourself but you must remove the tumbler, take it to the locksmith and have it matched up. This will only save you a house call charge. The screws to remove the lock are hidden behind the latch plate most of the time. Sometimes there are visible holes through the latch plate to access the set screws for the lock. Just the Norwalk tumbler needs to be swapped out, not all three. But the locksmith will need to know the key that it will be change too as well otherwise he may give you a 7 pin Schlage tumbler.