The setup isn't too good. For one thing, you should get rid of the sand and the under tank heater isn't necessary at all. Use just paper towel for babies as they can get impacted on any loose substrate very easily. Washed children's play sand is fine for older dragons and adults.
Make sure you have a good digital thermometer as two 75W bulbs can easily overheat a 20 gal tank.
The tank should be ok with two very young dragons for a little while, but no more than another 4 -5 weeks, depending on how fast they grow and if one or the other shows signs of failing to thrive.
If you are tight for money, pick up a clear rubbermaid or sterlite container at Walmart. These can be used as dragon tanks safely, providing you don't have other household pets or children that may want to get into the cage with your dragon or be a potential danger to them. If you do have such, look for used 20 gal tanks in the newspaper and aquarium places. Many places will sell cracked or similar tanks that can't hold water anymore for very cheap. I picked up a 20 gal tank for $10 from a petstore who was getting in new tanks for their fish/animals when they renovated last year.
Don't worry about getting a hood, though if it comes with one, that is fine. A screen lid can be bought for about $20 at most petstores or you can make one for about $5. Some 1"x1" wood at home depot plus aluminum screen and a staple gun is all you really need (some screws to attached the wooden frame. Pre drill the holes, as 1"x1" pieces of wood will split easy with a hammer. Alternately you could just use glue and those squiggly things used to connect corners of frames...can't think of these things, but basically it is a thin piece of metal about half an inch wide and maybe an inch long, bent to look sort of like the inside layer of cardboard (though closer to ruffle chips) and sharp on one end. You hammer these into wood near the corners to connect them. Whatever method you use, it is pretty easy to cut and build a screen lid that fits within the inner ledge of the frame of a glass aquarium (or you can have it overhang, but inside ensures the frame is rested on something solid).
You can put the basking light right ontop of the screen, though the UVB fixture will have to be attached underneath the lid (best way to do this is to have a wider sheet of wood in the middle of the screen cover, then you can screw the fixture to the underside.
You will also need to make sure the basking hood is attached to teh top of the tank securely, or clamped on the side of the tank,this way it can't be easily knocked off by a cat or kid and fall against something that could catch fire from the heat. A clamp stand could be used.
