Guinea shells are super hard and thick compared to chicken eggs, so that is normal (thin Guinea egg shells are not normal). If the keets can pip the shell... and they have enough humidity (which it sounds like yours did), then they can continue to zip and eventually get out if they were meant to. They don't always pip and then hatch a short time later... they pip, rest, zip a little, rest some more, zip some more, rest again, etc. With my hatches sometimes it takes 2 to 2 1/2 days for some of them to go from pip to hatch.
I open my incubators all the time (quickly of course), I usually just make sure to give the remaining eggs a quick mist with a fine spray mister bottle then close the lid. I don't think you messed up your hatch by opening your incubator, so don't beat yourself up thinking it's your fault.
There are lots of reasons why hatch rates can be low... still air incubators (especially the Little Giant brand) are less reliable and less stable than circulated air incubators, so maybe for your next batch you can get the fan kit for that incubator? I added a cheapo PC fan to my 2 LG still air incubators and use one as a designated hatcher only, the other I do use as an incubator when I need it, but I don't put any eggs in it that I'm really counting on hatching, lol. I have 3 better quality incubators (2 Hovabator 1588s, and 1 made by Fall Harvest Products) that are circulated air, with fans already in them and I get really decent hatch rates out of all 3 of those.
As far as it being too wet in the incubator... as long as the keets were kept at 98.5-99.5 degrees I doubt it would be an issue. Drying off in the brooder may have gotten them chilled tho... but it's hard to say. If you are concerned about the other eggs being too wet, you could open the viewing window, drop in some paper towels to soak up some extra water, close the wondow then reach in and grab the paper towels a while later after they are saturated.
Regarding how long to leave the last 8 eggs in there... I would wait until after the end of day 28, re-candle them and if you see movement put them back in and give them another day or so. I'd make sure for certain that they are early deaths before giving up on them, otherwise you risk tossing live keets that are just a couple days behind everybody else. I've found that there are warmer and cooler areas in incubators, so it is not at all uncommon for some eggs to develop faster or slower than the others. I usually rotate my eggs in the incubator each time I candle them so they are more evenly heated throughout incubation.
Good job on already having the Save-A-Chick, if you loose one at least you know you tried.
Hope you get at least a few more keets. Hang in there and good luck.