Without all of the answers, I have 3 main suggestions:

1) Try to get permission to ACCESS the private property to scout and track. I've had good permission getting access to walk most properties, even those I can't hunt - don't be afraid to ask...

If you can get permission, break up the birds either on the way to the roost or after they are in the roost. Once separated, be the FIRST hen to speak the next morning and hope he answers your calls. If he does, then you just exponentially increased your chance of calling him in for a shot. Set up as close as possible to his roost, and in the biggest opening in the pines that you can find. Decoy or not is a personal choice...

2) Hunt on the crappiest weather days or in the afternoon. If the pines are really thick, then I suspect the birds don't frequent the pines often, but might in really bad weather (where they can hear) or during the afternoon to escape the heat.

3) If you can't break up the birds, and have no luck in the afternoon, then get aggressive with your calling. I think you're past the point of soft and seductive...

Collectively, you're probably (99+%) trying to call the birds in a direction they normally don't travel during the breeding season. One of the only ways to CALL them onto your property is to sound like an old hen, one that wants to breed late in the season (which happens when they lose a nest). This can be deadly, but you probably only have 1 chance...
In essence, you're trying to draw the hens - the tom should follow - but he still may hang up out of range. This is where hunting with a partner can be key, as the shooter can be positioned 30-50yds in front of the caller....


Sum:
I suggest you break them up if at all possible, this will greatly improve your chances. You might be able to break them up without even going onto the property, but it will take a lot of racket...

Second to that, given your terrain, I think your best bet is going to be an evening or afternoon hunt - you may be able to swing them in your direction on the way to their roost...

If that fails, then get a partner and get aggressive, fighting purrs and clucks to imitate 2 hens fighting...