Can't you just have them sign before they leave, leave that paperwork with your advisor, mail it to her and have her email any comments? I imagine if she knows you need it done for a job, she'll be cooperative.
The BIG issue is: can you be certain to be done in time? All this other stuff is just blowing smoke, frankly, and can be worked out.
I received confirmation from my committee member this morning that she is willing to read the diss from abroad. What a relief! And I hadn't thought to have her sign before she leaves - that's a great idea.
And yes, I'm happy to say that this is a more than realistic timeline for me, and my committee chair agrees. Of course having a possible job is, as Mr. History said, an excellent motivator, just in case. Now to wait and see if the SC is still interested with these assurances in place. Thanks all!