A 55 with a good screen lid should be just fine. 40 is the absolute bare minimum i would go for an adult. Be sure to have all the right lighting and heat and so on, digital thermometer and hydrometer and all that good stuff . I would go for a semi-adult in that tank as it is a bit big for a young beardie, the smaller one may have an issue finding the basking area. I wouldn't handle the beardie for more then 1-2 hours a day tops and that is stretched over a few different periods. Being handled too much can cause issues from lack of basking(and the digestion of calcium if they arnt getting enough UV) and lower temps which can cause digestive issues and lethargy as well as temperature shock.