Chicks dying soon after hatching

[Chickquail army]

Ok this is for one of my cousins so I might not have all of the information but here is what I got,

She has chicken, button quail, cortnix quail and peacock eggs all incubating at lock down. The chicken chicks began to hatch and so did a few quails (about 8 in total) all with a perfectly normal hatch. Chirping and staggering around the incubator but 2 of the chicken chicks were on their backs with their feet trembling while the other two chicks were walking around the bator knocking the eggs over. All the chicks are alive and well (exept the two on their backs who couldn't seem to sit upright) up until yesterday when the two chicks turned up dead, a quail chick is dead, and 2 chicks still alive I'm the bator. One walking around almost dry while the other one is laying on the floor of the incubator. So far from today my cousin is left with 1 good active chick, 2 very weak newborn chicks, 1 also very weak seeming quail and another quail hatching.

Chick syntomes: they won't really move much, not even try to stand after a couple hours. When transfered to a different incubator to finish drying and to clean the other bator since it was beginning to stink, the chicks didn't resist. Laying on side no noticeable movement (if any) yet still alive. Normal hatch.

Incubator environmental: humidity between 80-90 (yes I know this is too high but I want to confirm if these things are the cause of the chick deaths or if it's something else)
Temp is normal 99/98

Other issues: since it's extremely hard to see into my cousin's incubator clearly, she has been opening it up (along with her sisters -.-) like once or twice a day (I believe) yes I know this affects the chicks but I find all these chick deaths strangly unusual since when I hatched my quails I opened it up like 3 times at hatch (when most of them were out to prevent smolthering)
Yes I know all these actions are mistakes but if there can be anything else besides this killing the chicks please let me know so we can help prevent all possible early chick deaths.
Also you are all welcome to post some hatching tips below.

 

[CWP1966]

Ok this is for one of my cousins so I might not have all of the information but here is what I got,

She has chicken, button quail, cortnix quail and peacock eggs all incubating at lock down. The chicken chicks began to hatch and so did a few quails (about 8 in total) all with a perfectly normal hatch. Chirping and staggering around the incubator but 2 of the chicken chicks were on their backs with their feet trembling while the other two chicks were walking around the bator knocking the eggs over. All the chicks are alive and well (exept the two on their backs who couldn't seem to sit upright) up until yesterday when the two chicks turned up dead, a quail chick is dead, and 2 chicks still alive I'm the bator. One walking around almost dry while the other one is laying on the floor of the incubator. So far from today my cousin is left with 1 good active chick, 2 very weak newborn chicks, 1 also very weak seeming quail and another quail hatching.

Chick syntomes: they won't really move much, not even try to stand after a couple hours. When transfered to a different incubator to finish drying and to clean the other bator since it was beginning to stink, the chicks didn't resist. Laying on side no noticeable movement (if any) yet still alive. Normal hatch.

Incubator environmental: humidity between 80-90 (yes I know this is too high but I want to confirm if these things are the cause of the chick deaths or if it's something else)
Temp is normal 99/98

Other issues: since it's extremely hard to see into my cousin's incubator clearly, she has been opening it up (along with her sisters -.-) like once or twice a day (I believe) yes I know this affects the chicks but I find all these chick deaths strangly unusual since when I hatched my quails I opened it up like 3 times at hatch (when most of them were out to prevent smolthering)
Yes I know all these actions are mistakes but if there can be anything else besides this killing the chicks please let me know so we can help prevent all possible early chick deaths.
Also you are all welcome to post some hatching tips below.

 

[CWP1966]

One time incubator user here. Pretty good hatch rate for the first time. 20 out of 35. I put the eggs in at midnight on a Saturday. 3 weekends later they started hatching at 6 PM Friday and kept on until late Sunday evening. The main thing is to not remove the lid or top. They can live 72 hours off their yolk. Wait until all are dry and fluffy and then have their brooder home ready. I used 2,50 gallon totes. Have the temp right. Reduce the temp about 5 degrees every week. They'll be feathered up and ready to go outside in about 4 or 5 weeks. These surprised me. I kept 12 girls and a rooster. Girls were laying at 6 months. 4 went broody at 10 months!!!!! Now I have dibs that are half Polish/ Bantam Americana, Easter Eggers. Oh yeah,the roo is white crested black polish. Didn't get any more Polish. These are Bantam Americana and Easter Eggers. All are gray in color. Going to be some wild looking birds!!!

 

[Pyxis]

Opening the incubator during hatch will not kill or hurt hatched chicks. I say this as someone who is in and out of the incubator all the time while hatches are going on. You run the risk of possibly shrinkwrapping chicks that are still hatching by opening it, but even that isn't an issue as long as the humidity doesn't drop too much and goes back up quickly afterwards. So that's not the cause for the issues.

Over how many days was this going on? From your post it reads as though this may have been a long hatch over the course of several days?

I do think that the very high humidity is the problem here. That humidity is just way too high. It is very hard to breathe in hot, humid air and 90% is extremely high. It's very likely that they couldn't breathe properly.

 

[Chickquail army]

Yeah, here is an update she gave me.

She told me that the chicken chicks started gasping (opening/closing beaks) and 3 more eggs (2 quail and a chicken) are cracked. The temp was around 32°C from yesterday. The humidity is down to 70.
Since she made the mistake of putting eggs at different times the hatch has been going on since monday.

 

[Pyxis]

I think it was a humidity issue. Make sure she's taking them out and getting them food and water, since it's been four days already since the hatch started. They can't go longer than 3 days without it and preferably no longer than 24 hours after hatch.

 

[CWP1966]

I was just saying that I didn't open it up once the hatch started. I had about 78% humidity. Before the hatch started I would open and candle the eggs about every day. Out of the 15 that didn't make it, they tried. Had their shells cracked all the way around, just didn't make it out.