Do what you can to make your bikes as quiet as possible, there are a few companies that make inserts for the silencer which will cut back on noise, with minimal power loss, but the nicce thing is, they can be removed when noise isn't an issue to get the power back. I know FMF sells them for around $50 which is well worth it if it keeps the neighbors from complaining.
Just have 1 or 2 friends over to ride with since 2 bikes are quieter than a group racing through the woods, and maybe once a month you can have a bigger group of friends over, and other times you can ride other places.
The important thing is to try and stay on the neighbors good side. Even though you did nothing wrong, go over to their house and apologize for disturbing them, and explain that it will not be an every week event, and what you plan on doing to keep the noise down.
I know it is your property, and you bought it so you had a place to ride, but i can also see the neighbors point of view. I have neighbors who party in their yard almost every weekend in the summer, It sounds like the music is right in the room with you (it wouldn't be as bad if I could understand the music, but it is all spanish music), and if we close the windows, all we hear is the constant booming of the bass all day long. It does get anoying after a while, and I'm sure they feel the same way about the noise from the motorcycles.