Here is what happened from start to finish--
Prior to illness and leading up to it (Christmas):
His first sign of illness was when he approached my sister in her bed (who he never approaches) and peeing on her bed in front of her. He still had all of his fur.
First week of January: He lost the hair from his butt and surrounding 3 inches of low abdomen first. He obsessively licked his butt until it turned red and bald

End of January/first week of February:
Our cat is peeing and pooing everywhere. His Maine Coon mane is nearly gone, chest and stomach are bald. His face looks miserable!

His fur is falling out on its own and he appears very itchy! scratches himself to bleeding in a couple spots on his body. his skin is scaly and peeling. He cries a lot for my sister. Major loss of appetite and weight loss by now.
February 10:
We bring him to the vet who prescribes Metronidazole, Revolution flea product (even though he's bald, sick, and has been treated for fleas), and a shampoo. The Metronidazole appears to hurt him more so sis stops it.
His urinalysis comes back as having elevated protein. His blood has high white blood cell count. And he has the symptoms mentioned in the subject line:
incontinence, pees and poos while sleeping
total fur loss all over body,
shedding patches of skin,
inappetite,
lethargy, stands without moving with lightless/dim eyes.
My sister can hop on and tell more as needed.
Please help us save our Bro! :'(