I would think long and hard about the need to re-take exams. I would only re-take something that is going to assist you in your chosen course, perhaps maths and physics. Then you might look for other qualifications that will build up your background education in a way that supports your ambition to fly, and which replace your missing A levels. I am not a pilot so I can’t recommend anything to you in this line but I am sure others will. Again as a non-pilot I don’t know if the lack of GCSE’s will make a difference to you. I can, however, give you some general advice.
Be sure of the relevance of any additional qualifications to your goal. There are a myriad of courses and qualifications out there and you need to find the ones that most closely match your objectives. I have spoken to people who have later regretted choices they made as they have subsequently found their qualification was not quite the one they needed. It may be that the ATPL’s etc are all you need.
Do not underestimate the commitment required to successfully study while you work. I completed a degree level diploma in management whilst working full time in a fairly high-pressure job. The University planned timetable suggested the course could be completed in 18 months although 36 months was the limit. It took me the full three years to do it and I handed in my last project on the last allowable day.
Consider whether your circumstances will support success. I was commuting to London at the time and the train journey gave me time to read a lot of the material. On the other hand things like getting married had a negative influence on the amount of work I could get done. I would guess that the flying training you have indicated in your post will be pretty much a full time occupation.
So in summary, develop a strategy, find out what you need (this is a good start) and put together a plan. Make sure the qualifications you choose support your goals and get commitment from your friends and family to help you through.
I sincerely hope that you achieve your goal. If you plan it well you will give yourself the best chance of succeeding. I hope this is of some use to you, good luck.