That is an unfortunate situation. I too have heard of similar instances, in one case there were several acres of buildable land and they put the McMansion right on the property line. It just doesn't make sense.
I do have a concern though about the Leyland Cypresses. They do grow quickly but they also succumb to diseases quickly. I would encourage you to interplant them with another variety of evergreen that might grow more slowly but live longer.
