buy a couple plastic containers that are long enough so each dragon can be stretched out with their tail curved comfortable about half way down the length of the tail. These should also be wide enough that the sides of the dragon barely touches the sides of the container or there is some space (this is with the dragon lying down) It should be a few inches deep but not too deep. I have seen containers like this in Dollar stores.
The box should be lined with styrofoam (the denser foam sheets used for insulation are better than the bead foam but either works) including a piece on the bottom and top.
Use as large a box as you can, this way it is easier to ensure a constant temperature inside the box. A too small box can change temperature alot faster.
For packaging dragons I find its best to wait till night time, while they are sleeping, gently put them into the small container, then into the box, or just keep them in the small container before putting them into the box. (this ensures the whole packaging part is less stressful. They are asleep and if they wake up during the day and see its dark and cool..they will just rest. There are dark cloudy cool days in the middle of summer all the time. Of course have air holes in the container. You shouldn't need any in the packaging box at all. Big holes just let heat/cool escape.
Oh in the containers, you can line it with paper towel, newspaper etc for padding. Around the containers in the packaging box, use crumpled newspaper or other packaging 'filler', especially any that allows good 'breathing' (ie don't wrap them up in bubble wrap).
Before boxing up your reptiles, make sure your courier/airline etc. actually accepts harmless lizards. Make sure they understand these animals are alive and can't be too hot or too cold.
As for snake bags or pillow cases, I don't' recommend that for bearded dragons. Their spines can catch on the cloth and this will be uncomfortable and painful for them.
-----
PHLdyPayne