You can do it, no offense to Mr. T, but you don't HAVE to do the pan underneath, but it's a nice to do thing.
It will really depend on the shape of the birds, you just might do a little dry run will they're still wrapped up. Place them inside and make sure you have airspace.
OH... and 1/2 through the cook rotate the birds, top to bottom bottom to top. The one on top WILL dripp on the bottom on and since you don't have a pan
catching the juices, the other bird will.