Oh, sorry, I didn't read the whole thing, so I just talked about dehydration mostly.
Fastest bonding that I've had with my rat is not just giving treats but 'how' I give them: I spoon feed him.
There is a great rat author named Debbie Ducommun. Libraries should have her books; you don't have to buy them--great advice in there.
Get a baby spoon, the kind coated for comfort, then get a sampling of baby food (Beechnut, Gerbers, whatever): Carrots; squash; beef; bananas; apple and so on, concentrating on veggies and fruits (the meat is great for enticing the ones who don't want to go back in their cages to do that).
Mannie was not associating me with the food I gave him like slivers of apple? He just 'stole' the piece, ran and hid from me to eat it.
Once I started spoon feeding him and making sure he had to reach just a little past my other hand to get the spoon--give yours a nibble or two first without making them reach, then make them reach a little further--no rush, be calm, sweet talk them by name... And in no time you will have them placing their back legs or front arm on you for balance while they eat from the spoon.
Do not let them take the spoon away from you
Now, they will associate you with the food; they will have your scent on them; they'll hear your voice and associate it with the eating 'while' they are eating; and they can't just run away to hide, keeping scared habits going.
Also, feed them one at a time, not letting the others out--just pick one out to spoon feed, spend a few minutes talking and feeding, bonding with; put him back and coax out the next one, repeat until you have done this with each one:
No competition this way, less likely to have a poop fest.
I've only got the one so far and he has never had loose stool or panic poop.
He was very skittish at first, then less so, now still less...
The progress is fast (though not what I had with cats), and I'm sure it's because I have only the one.
I am, however, starting this weekend, going out with my husband to find him another male buddy--preferably a younger one so Mannie knows he is boss and the baby will too--less chance of bad fights.
Sneezing actually can mean they are displaying Myco; most rats have it.
The only ones I have read who do not have it (if it is still true) are laboratory rats (staff sometimes will let you adopt one or more they are going to put down); otherwise, the Myco is dormant; this is what all experts I have been reading say: It is just the way it is, now:
So, have them checked by a vet, of course, but you keep an eye on them looking for lethargy, runny eyes, sneezing, general signs of illness:
Keep them cool (60 to 85 MAX Fahrenheit), plenty of water available (fresh; change it at least once a day; as you have more than one rat--and add the ice).
I don't try to pick up Mannie.
I did that ONE time and it was a mistake--it made him distrust me, and I had to work to earn some of that trust back.
Now I understand that going slowly, giving him spoon fed food and making him reach for it, lying down so he can explore my body and get my scent on him, and even letting him take a long piece of favorite food from my mouth (which he enjoys doing) is a better way to bond, build a solid foundation.
It would have been ideal of course to get just weaned, very socialized rats (two males) but that is not how I got mine: I fell in love with a feeder in a pet store who was gonna be snake food.
He was separate from the others lying all over each other; he had one hand up on the aquarium glass and he was watching me right in the eye. So I put a finger in next to him, carefully, slowly and left it there. He sniffed it, then he licked it. That was it--I said 'I'll take this one!'
And Mannie didn't get eaten by a snake. He got adopted by a rat lady, instead. (✿◠‿◠