Really the only thing you need to know is what you've figured out already - the headsets work with IR emmiters built into the entertainment system of the van. There appears to only be one "standard" and searching for "Dodge Caravan IR headset" will give you tons of choices.
The only thing I would look at is to make sure the headsets are "dual channel" capable. My van has a dual DVD player so the second row can watch a different movie than the third row. The headsets must be able to handle and separate the two signals for this setup to work. Maybe all the IR headsets are capable of this and some vendors advertise it heavily while others don't. The aftermarket headphones I bought have a simple 1/2 switch to pick a channel.
Note that the same headphones will also work in a VW Routan since it's just a re-badged Dodge Caravan, complete with the same DVD entertainment system.