Hi Melinda! My mom has a cat that also has a funky area right above the tail. He's an overweight red tabby. There are lots of dandruff like flakes and a ton of hair. I'm convinced that he's too "big boned" to reach it. Without them being able to reach hair accumulates and the flakes. Ours doesn't have scabs like your kitty does, though. I'm thinking maybe your cats may be due to flea bites. Or, you may be right about the other kitty picking on him. Is the other kitty the aggressor? If so, then the boo boos would make sense because he would be running away-hence the injury to the rear end.
Other than Sookie's condition , hope things are well with you and your partner.
First Spike could have been up to no good and bit or scratched Sookie causing inflammation and perhaps a bit of cellulitis:
The signs of Cellulitis is:tenderness to pressure, spot feels hot, hardness(,not as soft as the area should be), and change in color (redder than it should be. Check for enlarged lymph nodes and red streaks in the skin.
If this fits the bill than locate the infected area and clip the hair away and apply hot saline soaks 3 times daily( 1tsp salt to a quart of warm water.)
Second : When you part the hair on top of the tail is there a brown waxy material. If it is infected it will have a rancid odor and make the hair in the area very greasy. This is called Stud Tail and can effect (Studettes) Their is a wash of Tar and sulfur for this but check with your Vet before going any further. Could also be feline acne, folliculitis Inflammation of the hair follicles or God knows a number of other skin conditions. I guess it best to have the vet take a look and a skin scrapping to diagnose properly.
.....and if you think I wrote all of the above from my brilliant mind, you'd be Soooooo wrong. I have a great book "Cat Owners Home Veterinary Handbook". It has helped me out in a lot of situations.
Please let us know what is going on with Sooki after she is checked out--maybe give Spike a Time Out, LOL!