My response is not a professional one just and observational one considering what you have stated.  There are 4 lots- good, that's what it takes to form a road association.  Problem is, seems like the developer owns 2 of the 4 lots still so an impasse is likely the best outcome you could expect at this time (you need 3 of the 4 to call a meeting begin the process for setting up an association.  Yet still your deed says you have a declaration(what legally that means, I don't know) indicating an agreement "will be entered into...".  If the deed say "agreement" and you have none.  He could plow away and you might not have any legal responsibly to pay a bill you have not "agreed" to.  Of course that would be impracticable if the plowing stops and you are forced to do it yourself at your own expense.  You mentioned something about other issues and I assume both sides may be enjoying the battle more than searching for a mutually beneficial solution.  

Once the other 2 lots are sold, I doubt the contractor will be in the picture any longer and you may have to wait until that happens.  In the meantime you also may obtain a couple of other estimates and present them to the contractor for agreement- he/she won't, of course, but you may be able to recover excess costs after they are out of the picture in small claims court. Anyone acting for the group, I believe, has a fiduciary responsibility to do what a reasonable person would be expected to do.  If the cost/service is dramatically different, you have a complaint, if your concerns are minor compared to the delivered service then your real problem remains the "less than amicable relationship".