I have a different kind of car seat. I'm honestly not sure if you can attach two harnesses or not, but I don't usually hook up Lexi because I don't feel it's necessary in this type of car seat.
I have the Cozy Cabin. I'm not sure how it would fit your two dogs. Lexi is small, and two dogs of her size could fit. I got mine on eBay for $99 and free shipping.
Kittywalk Systems
I took a picture of Lexi in hers, but I didn't download it to my computer yet. I can try to post that picture if you need it.