I don't understand the Y part either. Sounds like you should have a straight Tee coming out, with a slight flair - couple feet each way - to allow turning onto the public road.
As well, I don't understand the maintenence deal - you all 3 use the road (I know you said you don't, but it's there for you to use....) so everyone chips in 1/4 and maintain it that way. Not just th epart on your property, but everyone takes care of 1/4 of the whole road. Now I understand you doing it the way you are doing it, and not looking to bill anyone - I get that. But, the whole deal is set up wrong......
I think you got one shot at this, keep it civil but make your statement strongly.
A snow fence and maybe seed some grass next spring - well a truck trailer can drive over that pretty easily, I don't think you are making much of a statement at all.
A boulder or other immovable object is the statement to make, fisrt time, and will be the best chance of making things stick.
Where I live, there are rules how far away from the public road such a thing could be, and there are rules how wide the access road (easement accross your property) has to be. I'd think that would be a 20 foot easement here, if not more, and place the rock where you are allowed to place it. If you put it too close to the public road, etc. then tyou will be forced to move it, and will have lost your statement.
You need to make a calm but very firm statement.
You are also in the middle of a family fued. If he didn't get along with his sis, and you own his sis's land, then he is carrying that grudge against his sis, and how his grandma treated him 0 he is projecting all that dislike onto you. Once you start messing with the road, it'll bring up all his bad feelings about that old situation.
Good luck with all that. I think you are right and correct, but lotta good that does you.
--->Paul