I did all my ground school with a specific ground school instructor, as I felt this left my flying instruction time better used for learning the practical flying skills. We worked through the subjects one at a time, and did the exams when we thought I was ready. Of course I was still studying at home, and picking up the tips and pointers from my flying instructor. Whilst this very skilled teacher has now retired, I used to see adverts for ground school instructors in pilot magazines so maybe this is worth looking at?
You may find that one on one teaching is better for you to absorb the information than just reading it from a book - I know I did!
Don't forget that the multiple choice exams are set to trip you up - so make sure that you have read and inderstood exactly what the question is asking, not what you think it is asking from a quick skim!! There is plenty of time in all exams (apart from maybe the nav exam) so check all your answers at least twice.
I think that you could probably make the 22nd to retake air law, but you should be studying every moment you have. Bear in mind that each exam does overlap a bit and cover other subjects so you will need to know air law when you take your other exams!
Good luck,