The easiest way would be to tape the Horizon regular boxes together. It would take 2 different sets of 3 boxes taped together. 6 adults in 1 set (2 per box). In the other set 2 adults in 1 of the boxes and divide up the 1-2 month olds between the other 2 boxes.
Until you pay the cargo shipping on those express boxes, its cheaper in the long run just to buy some of the 2 bird boxes. I can get them as low as $7/box and sometimes even free shipping if I buy enough of them. Even if you figure $10/box, it would take you 6 boxes for a total of $60 just for them. Those Omni boxes are about $25 each roughly and they charge through the nose to ship them too.
When you estimate the express mail, go to
www.usps.com and plug in the zip codes and box weight/sizes. It will be a little different for each location. When taping those boxes together, the measurements will run about 16" tall x 10" long x 24" wide (8" for each box). Generally it runs right about $90-95 for those.....
If shipping that many birds, without having an accurate weight or the zip codes, I can give you a rough quote.... It will be about $180 for the express mail and $60 for the boxes. About $240 total. Its ALOT of birds!!! When you figure 1 pair is generally about $60-65, it still better to send more if you can.