I made a window insert that's similar to a wire panel for an aviary. It keeps the beaks away from the regular window screen when I want to open the window. I usually keep the blinds down so no one can fly into the glass or the wire, but if window wasn't covered it would be safer for a bird to crash into the wire than to crash into glass. You need to keep the glass covered up for safety, but you wouldn't have to cover up the wire panel.

Here's what it looks like. I open the window, put the screen in place, then slide the window against it to hold it firmly in place:


Here's what it looks like with the blinds down.

Very nice, but you might have some insects that come and visit this way though...

The ordinary fine-mesh window screen is still there so no insects will be coming through lol. The hardware cloth screen is in front of the regular screen to make sure that the birds can't reach the insect screen, chew a hole in it and fly outside.

ah, that's what you ment with 'regular window screen'...

I didn't get that.

thank you. I thought window is only one of the hazards. I thought they could run basically into anything - a wall, an open wooden door in the house or even into each other (sometimes they almost run into me). I thought you would be suggesting to clip their wings
With the large sliding door I have in the living room, the way I usually have it set up : one half would be glass while another half is insect screen that is kind of soft. There is a small decal on the glass part + blinds at the end of the sliding door. I would hate to keep blinds covering the sliding door even in an open position - it will be like nighttime, my house is very dark.
Hmmm, behind the insect mesh I either have closed glass door if I run AC, or nothing on a nice day like today. Yes, they can possibly chew a hole in it but I never seen them approaching the screen for anything. IS there a possibility? it's kind of metal, soft but still it feels metallic.

When a bird poos large poop at night (vs many small poops), should I consider this birds a girl or not necessarily?

Any bird can make large poops. Especially when nesting because they hold it in until they are out of the nest so that they don't get it dirty.

You could certainly clip their wings if you wanted to. It doesn't have to be an "all or nothing" choice between being fully flighted or basically non-flighted. If you took just a few feathers on each wing (like maybe three) they would still be able to fly, but it would slow them down somewhat and they wouldn't hit as hard when they ran into something.

I will need to be gone for one day and one night
Hubby is concerned he won't be able get birds into cage when it's a sleep time. I suggest to remove all the food about an hour before bedtime and then put it into cage only.
Actually today they all were in the cage at 9 without me doing anything at all. Except Cuddles but for me she is easy. But you never know what cockatiels have in mind ( we already heard it today:)
In case they don't cooperate, would it be OK to cover whoever are in the cage but leave some others out and keep some light on or is it a very bad option?

It would be safer to have them all in the cage, but if there's a bright light on all night with them out of the cage it won't be particularly dangerous. Having them out at night in a darkened room would be VERY dangerous if they have a night fright.

Since you're only going to be gone for one day and one night, why not just keep them all in the cage while you're gone? They won't like it but they'll be safe.