Do NOT quit.. Not saying you shouldn't look around in your spare time looking for something else to do.. What doesn't kill ya makes ya stronger... You'll learn valuable lessons learning how to put up with your current situation.. 

Adversity brings out your character.. You'll find out what you're made of... Hopefully you'll pass the test and a door will open up to a wonderful new opportunity....DON'T burn any bridges...

If in fact it is the complete fault of your employers, it'll catch up to them--they'll lose ALL of their help, or have a bunch on imcompetants running the show...with the resultant loss of business.......Then, you can step back in, and run the show......

Good luck........

Inspect yourself very carefully and impartially... Be absolutely sure it is completely their fault...A poor performing employee will get mistreatment- even subliminally....