REI half dome.

2 entrances >Yes
2 vestibules sufficient for a good sized (i.e., 70-80 litre) pack >Yes
Vestibules which allow opening/entry without getting the inner tent wet >Yes
At least a partial-fabric inner tent (i.e., not all mesh)>Yes
Vents in the rain-fly >Yes
Wide enough for a couple Therm-a-Rests for the full length of the tent >Yes
Under 6 pounds >Yes
Around $300 or so (preferably a little under)>Yes

I own lots of tents. I get to see lots of tents in use. For what you described my number one pick is the REI Halfdome.