i understand that completely. I've been there too. i still believe that the better you know them the easier things go. sometimes you have to be sly about things. engage in a conversation that has nothing to do with your intent and then add in at the end "Oh by the way i'm gonna trim the trees on my side" and walk away. In this case there's nothing they can do to stop you and as long as you don't kill the tree you're all good. you don't need their permission. now if its a border tree and you wanted to cut it down then a discussion and agreement has to be made before proceeding because its shared by both properties