If your teachers are really that bad, don't worry about them being mad at you, do what is right for you. If anything, you should be mad at them (although don't deliberately upset them, you're still trying to get an A level out of that school). If they'd have bothered with you you wouldn't be in this position anyway. Always do what is right for you in any position like this, its your future.
Further than that, I'm not sure I could really say, but to me what your saying sounds reasonable.
Edit: so long as you do as much of the coursework for the subject you are keeping I guess. Also, not sure if you have to disclose the failed A levels on your application form (really not sure here), although if you're going to fail them anyway (hence retaking at another college) then maybe doing the coursework for a subject your definitely going to fail isn't wise? See if one of the teachers at your new college could give you some advice perhaps?