We have a mini and a regular. I could be wrong, but I do believe they stopped making the mini. The last I checked (4 months ago or so) it is not on their website.
Sachi is 4.3 lbs and fits in the mini just fine. The regular is very roomy for her. I can see it fitting 2 very small dogs, but they may have a hard time moving around.
These pics are before we got our Jaraden carrier. We used to take it in and out of car when she's with us (which is most of the time
). Now we just leave it in the car. Very secure as a car seat!
MINI
REGULAR