1.) Talk to them. You *have* explained your problem to them, right? Show 'em the map, explain how you need to get to work in the morning, etc. Explain (politely!) to them that you're going to have to talk to their mortgage holder if they can't obey the terms of their deed.
Failing that...
2.) Figure out who holds their mortgage (via the public records office). If you're lucky, it's a local bank with folks you can actually talk to. Explain the situation to them--the bank will care, because an easement snarlup would make it tougher for the bank to sell the property if they had to foreclose. The bank will call them, and they will listen. If you're unlucky, the mortgage is held by "MORTGAGE ELECTRONIC REGISTRATION SYSTEMS" (MERS), the mega-conduit the big stupid firms use to hide ownership of the mortgage, and you're unlikely to find a real human who cares (your neighbors may not know this, though!).
Failing that...
3.) *Now* you're going to need that real-estate attorney (I am not one!). Have the *attorney* draft a letter explaining the situation in intimidatingly baffling legalese with a very clear last paragraph--"Do not block the access easement, or there will be legal consequences."
Failing that...
4.) I think you're going to have to get a (civil) court order enforcing your access. If the neighbors still block you, *then* the police can enforce the court order, or the judge can hold them in contempt. This is both expensive and annoying to the neighbors, though, and almost any sane person will do the right thing before that.
