ISS AVMan

Hello, I need some input on the best way to handle a situation. I have an existing INSTEON/ISY994 customer with a 4000 sq/ft house. He is building a 2000 sq/ft guest house on the other side of his pool about 250' from the main house. The guest house will be fed with a separate electrical service, but fed from the same transformer feeding the main house. The owner wants to be able to control the lighting path from house to house that is around the pool area. Do I wire the path wiring with standard switches (3-ways) and give the guest house its own ISY994 because of the distance? Is there a way to make 2-ISY's talk over the network if I extend the network to the guest house? Any ideas?