It would be alarming if a lawyer and his client were using facebook for privileged communications. That's your first hint you need a new lawyer. If they can't understand Facebook's TOS they can't possibly defend you.

But, seriously, these are foreign nationals. We've had a longstanding distinction between foreign and domestic surveillance. Think of it this way, would you really want to need permission from Pakistan to surveil Osama bin Laden? He was an enemy of the USA and he was being harbored by Pakistan. Different rules apply in that case than in a domestic case.