Hi Dave,
I guess you didn't look at the link I sent you, so I will try to explain it.
No, they are designed to work in pairs. This keep the technical level the same and ensures that there
is no problem with one end being too low a signal strength to cause problems.
In your case, the the distance between the two will be close enough that you may be able to get away to
using only one on the roof to your existing router, but no guarantee.
The advantage of the Nanostation series vs the bullets that I use is that they have an integrated antenna.
The range is only a few miles, but obviously not a problem in your case. Since they function as a bridge,
the one on the roof can replace your existing router there, if one is already installed.
As you will see on Amazon and other sites, they are very reasonably priced.
I hope this explains it.
73,
Mitch DJ0QN / K7DX