I ended up using a cardboard box and it worked wonderfully. 5 of the 7 eggs hatched and the baby birds are now all grown and left the box by themselves!
One accident happened two days ago. First one baby bird escaped through the bottom of the cage (I have big cage in patio). The dropping tray was not aligned well so there was a big gap. with one bird gone, I tried to adjust the tray but their cuttle bone fell and got stuck at the bottom. When I reached in the get the cuttle bone, another baby flew away~~~
I was worried.. but guess what! they both came back the next day around noon time and eating the seeds on the floor! I managed to catch one with a net.. but 2nd one flew away so fast. Later on it came back 2~3 times, hanging onto the cage, but I couldn't get close to it.
The 2nd night passed. This noon, the bird came back again. I was happy. and I tried and tried to catch him. I actually had him in the net once the the holes were too big he escaped. but finally! this afternoon I got him! but i guess he's got a smaller body, so after i put him back to the cage and looked back.. he's outside the cage again! It scared me half to death but I got him in again.. i hope he's now feeling happy with his parents and siblings and will not try to escape anymore!
So thank you all very much for the advices and support. I am glad my birds are fine and grown

But last question... Will the color of their nose change as they grow to reveal their genders? (blue for male and pink for female).. or the color is just what it is when they are born?... i am asking because i see all of my 5 baby birds have pink nose..