I'm sorry, you're getting out of my legal depth here.
I'm sure you know that winning civil legal arguments is about constructing arguments based on opinions and interpretations, drawing on previous case law as precedents.
The Statutory Declarations have presumably given you an easement based on the Prescription Act (minimum 20 years use, without permission). I assume this is what has been registered onto your land Title Register. If it isn't too long and you want to write the wording of this part of your Land Title onto here I'll take a look, but I suspect you are going to have to employ paid-for legal advice here.
Strikes me these people seem pretty determined.
If you are going to seek legal advice, perhaps you should consider going back to the original solicitor who acted for you on the purchase - if this was done incorrectly they have an obligation to sort it out - or have action taken by you against their defective advice?