Aussies are a lot of maintence... they can be temperemental... and are known to bite... and bite hard. Not all of them do it, but a full grown male can deliver a nice bite to your hand. They also have to be wintered, they hibernate, and in order to keep them healthy they must be cycled.
Honestly of the two i would suggest the CWD, chinese(green) water dragon. They can be VERY shy, and skittish, but rarly ever bite, they are very tolerant of people, but when they do bite, its more a warning then it is to actually cause harm. I've only been bitten once, and thats because i had my fingers near her mouth trying to dislodge some junk off her face.
Yes they need UVA and UVB.
http://www.triciaswaterdragon.com
This website is the most complete care guide you'll find on the internet, i suggest reading the entire thing before purchasing your CWD.
It is better to get one dragon first... wait till its full grown, then get the second.
Just remember if your going to get them, be absolutly sure you are willing to take them to the vet. It'll cost you anywhere between 50 - 120 dollars... (usually its 50 to walk in, 30 for a fecal (poop) check, and the rest could be medications or such. If you aren't willing to take them to the vet, you really have no buisness getting any pet.
dehydratoin, and parasites are the two most common ailments in water dragons. If the skin is wrinkled, they are dehydrated. Parasites usually cause loose stools.
If you get them, try and get them at atleast 12" total body length. Yea, you might want to watch them grow up.. and all. But the bigger they are, generally the better they do. And at 12" it is sometimes possible to identify males. Its not a sure thing, but if you know what your looking for it can be possible. (the femoral pores on males at that size will be much larger, seam more like bumps, and have dark pores in the center of the scales)
Water dragons typically lay about 8 eggs, 1-3 a year.