The model they list as a possible two-person would be the Safari: HENNESSY HAMMOCKS: Catalogue ultra-light line of jungle hammocks, ultra-comfortable camping hammock/chair/tent hammock
(about 1/3 of the way down) I would note that the description mentions two in the hammock, but it is not the purpose of the hammock. I don't own this model, but I question how well two could get in there with the way these particular hammocks lay. (Can two fit in that flat spot that goes diagonally across the hammock without going insane?
A few points come to mind. This hammock/tarp weighs 4 lb. 8 oz. You can probably drop over a pound by just seperating and going with two different hammocks/tarps. Now add in the insulation, and it may be a bit more , as you could now downsize your quilt/underquilt to fit your fused togther bodies. Sounds kinda hot....right?! But--
Laying in a double, I have found the two of you will tend to gravitate toward the center of the hammock. It is difficult to reposition yourself. Everytime someone gets up, the other wakes up. Do you really want to be pushed toward that stinky thing all night? (Perhaps you GF smells like roses on the trail, but not mine! Sorry, honey...<smack!> )
Now compare that to using two singles where each of you has their own space. Each of you gets the sweet spot of the hammock. You can stay up longer without bothering the other person who wants to sleep.
There are quite a few folks here who have slept in their hammocks with their kids. I think that may change things because now you basically have a regular sized person, and probably a 1/2 sized (or so) person in the hammock vs. two full sized people. But, these folks may have some insight with regards to techniques or hammocks that they reccomend.
One question right off hand would be, are you all planning on spending all night in the hammock, or just napping?