LG Bator, digital hygrometer, but still nervous! -updated on Day 19!

You all seem like nice advice-givers... I'm a pre-K teacher... this is my 4th year of attempting a hatch! Any advice would be appreciated as I have lots of excited students and don't want to disappoint!
Here's my story:
1st year: rented a bator and turner. Had some trouble with temp consistency, but had 3 out of 12 hatch - several chicks made it to the end but died in their shells - I think I opened the bator too much ... oopsie, newbie mistake!
2nd year: rented a bator - the turner broke halfway through, and had to turn manually. 2 out of 12 hatch.
3rd year: got a new LG still air bator and turner! No problems I was aware of, but 1 hatched then died the next day, 2 more had pipped and got stuck facedown! Tried again with another 12, this time water kept evaporating quickly it seemed... 3 out of 12 hatch... 5 more looked to be developed when candled...but not even pipped.

This year - using the 1yr old LG bator and turner. Got 11 eggs, mostly Rhode Island Reds and something starting with an A... also one "Blue". Bought a cheapie digital thermometer and hygrometer - I salt-tested the hygrometer and its pretty perfect. I put the eggs in at 10:30am on Wednesday, so today was day 6, right? The temp is at 99.5, however, when I came in on Sunday, the temp was down to 96!! (when I left school on Friday, it had been 99.5). Humidity has been pretty consistently at 60-65%, I've only had to refill the water 2ce. If I take one of the plugs out, the humidity goes way down, and someone recommended that I leave them in until day 18.

So here's my questions:
1. When should I candle them? Last year I did it 2-3 times, I think if I only candle them once, it might be better for them temp-wise, right? When is the best time?
2. Did being at 96 degrees for possibly a day or two kill some/all? Please say they're fine! Ugh!
3. Is it okay that I'm leaving the red plugs in for now?
4. What else can I do at this point to have the best possible hatch?
5. I'm considering carton-hatching this time around, as last year I had two get stuck facedown. Any thoughts?

Thank you! I'm one of the only teachers at our school who has ever tried this, and I'm starting to get the reputation as not having much success!! If things don't go well this year, I am afraid of trying again. Please help!

 

Thanks, everyone!!
I do think I have to disagree with the heating problem.... I live in southern California, and we rarely turn the heat on at all (don't hate us, I know!)... we haven't been using it at school the last few weeks, so I know that wasn't the problem. What I was thinking it that I must have bumped the temp increase/decrease knob when I checked on them Friday before I left school. I know no one unplugged the unit, and it's not near a window, so I think that was probably my fault and hopefully won't happen again! Will a day or two at a few degrees under hurt them too much?
I will try to get the humidity down a bit. I know there's mixed views of humidity, but the woman who gave me the eggs seems to believe that one ring should be filled with water, so that's what I've always done. Should I take the red plug out? Or for part of the day?
Thanks for sharing in my journey. I really do need the hand-holding, I guess!

 

Oops, it is a forced air incubator, I guess...and it says right on the incubator to keep the temp at 99.5 As far as getting a new incubator, well, this one was donated by the person who supplies me with the eggs, so I'm kinda in a position where I need to give it a fair shot. I'm only trying this one round this year... no matter how this goes! If I have any success, I'll do it again next spring.
As far as the temp goes, my classroom stays pretty warm, even without heat. It's upstairs and I highly doubt the temp in the room fluctuates too much - I've been there at night several times and it has seemed fine. Humidity is more my concern as it is very dry here year round.
I'm thinking about candling them tomorrow night just to see where we're at... do you think it's too soon?
I originally had read that the humidity should be 60-65% for the first 18 days, then 70-75% after that, so that is what I was doing. Today I positioned the red plug half over the hole, and it is holding somewhere around 57%. Better? When I take it completely off, it drops to somewhere around 30%.
Thanks! Any continued thoughts are appreciated!!

 

Okie dokie... an update - I candled the eggs tonight - end of day 8. One out of the eleven is completely clear, so there's a definite no go there. At least 7 look like there is definite growth, a nice air bubble, moving mass, etc - two are kinda iffy - they have darker shells and its harder to tell. At least there's hope!!
Here's where I'm totally in wonder: One has the air sac on the bottom - what the heck is that??? I put the eggs in exactly as she gave them to me... pointy end down, but this one looks upside down! It's pretty oval in shape, and hard to tell which end is pointier, but it is possible that there's been some growth even though it's upside down???? And maybe I'm looking at something incorrectly, but it looks like a completely upside down version of what I'm seeing in all the other eggs. I had another teacher look with me, and she agreed. So... will it definitely die? What if I flipped it now? It really looks like something is in there - I see a dark mass moving and everything. Hmmm....

So, I'm working hard to keep that humidity in the 45-50 range... if I close the vent plug, it gets into the 60's.... with it out, it's closer to the 30s... so I have it still half covering the hole, and that's what keeps it the closest. Temp is doing great now though - I've stopped touching it!