It might be that I'm a bit younger than you fellas, and a bit more hot-headed, but if it was me, I'd just sit down with the owner of the land you hunt on, and discuss the matter with him. The owners to the north of you have made it clear that they don't want to work with you on the matter in any way, shape, or form. The son seems to have a bit of a selfish streak in him "claiming" all the deer in the area for himself. While I get a bit frustrated with people hunting close to or crossing our land, I know that the deer will be back, and if not...it just wasn't meant to be. Hopefully the son will grow out of his attitude problem, but from the way that the father sounds, maybe he won't. Just talk with the guy who owns your hunting spot and tell him what you plan on doing so that when/if you confront the neighbors again the landowner is on the same page as you, and has your backing in case it does come down to the game warden coming out and writing citations/warnings. Hope this helps.
~~~Amos
Oh yeah, and the comment about making sure they drop on your land is a good one....while it messing up a bit more meat, shooting the deer in the upper shoulder should drop the deer where it stands the majority of the time.