would they make sound if they were hungry? when they sleep, do they lay down on their tummy?
I am seeing parents cuddling together. Hope this doesn't mean desire to mate and lay more eggs.

I am scared about feeding them. I am expecting to receive new formula early this week.

Crops looked full when I got them out of the box today. Does it make sense to weight them with full crops at all? the weight doesn't reflect the true weight, right?

But, what alerted me, two youngest chicks both had only one eye looking at me. It looked like something was preventing another eye from opening. I didn't touch the eyes, I hope there is nothing serious. They all were a little bit sleepy at that time. Anything I can do about it???

With parent-fed babies you pretty much have to feed with a full crop, since the parents don't let the crops get empty. It won't give you the true weight, but you'll be able to see whether they're gaining weight at a normal rate.

Yes, babies often do lay down to sleep. Cockatiel babies should be on their bellies with their feet under them, not on their backs with their feet in the air. There are some parrot species where the babies do sleep on their backs, but it's abnormal for tiels. If their heads are on the ground with their necks stretched out, that's normal too.

If an eye seems to be stuck shut you can gently wash it with warm water and a soft cloth or a cotton ball.

better to do it now or can it wait til tomorrow? its 8pm here.
Cotton swabs won't work? (what people call Q-tips)

It can wait until tomorrow. You can use a cotton swab if you're confident that you can control it well. But it's basically a pointed object even though it's soft on the end, and if your hands aren't steady you could poke the baby's eye with it.

thanks, I won't use it. What can be causing eye not to open?

Did these babies previously have both eyes open? Sometimes one eye can be slower to open than the other, but gentle washing can help release it. If both eyes were previously open, it's possible that the babies were just sleepy and didn't bother to open both eyes.

the previous time the youngest didn't yet opened eyes at all, and I can't remember about the second youngest. Didn't pay attention I guess. I will look closely today and I hope they just opened one eye first.

Looked at their eyes today. The youngest doesn't have any problems but his older sibling does. It looked at first that the slit that cut the skin open isn't a straight line but rather some zig-zag shape. Then I decided to give it a try and clean it with wet cotton ball, and it helped. He opened his eye round but there is still a small particle in the very corner that I couldn't clean. I will look at it tomorrow again. Also, water cooled down while I was looking at him, hope its not a big deal.

He'll probably be OK but keep an eye on him. A small amount of cool water on his face shouldn't do any harm as long as he stayed nice and warm overall.