I am afraid you are looking for an answer that doesn't exist!
There are no quick and easy routes into the pinnacle levels of this industry. Even those that might be regarded as such are fraught with their own difficulties, be they financial, selective, competitive or whatever else.
It is certainly possible to become an airline pilot without educational qualifications, however in this day and age it is also very unlikely.
My advice would be to retake your GCSE's in any event. They will stand you in good stead whatever you route in life you are likely to embark upon. I appreciate that circumstances may preclude full time education, but plenty of people utilize part time colleges, correspondence courses, and self study to achieve this form of self betterment. If you think this is "humiliating" and you have "ability" and "potential," then do something about it!
Bearing in mind the illness that prevented your secondary school completion, you might also want to research the medical requirements for commercial pilots licences.
I am afraid that it is a harsh reality, that competition in this (and many other) industry is fierce. There are a lot of very good, qualified, and well able people, chasing a very small number of opportunities. Whatever may or may not be the realities, this is viewed as a highly desirable occupation, and in turn it attracts a spectrum of hopefuls, many of whom are likely to be disappointed.
Employers (and certainly airline employers) do not usually offer interviews to anything less than their perception (note, not yours) of the most likely candidates to prove successful. In the case of airlines, there is not a single candidate in that category who will not hold a professional pilots licence. They look for far more than that. They will certainly expect to see a solid educational background. Where there is a minimum educational achievement stipulated, that is your clue as to the levels they are likely to be seeking as a minimum.
You don't need any GCSE's or other specific educational attainment to embark on a PPL or any other licence. However certain programmes and many employers will set such stipulations. People will (often rightly) tell you that such qualifications carry less weight once experience has been acquired. Of course this is a catch-22 in that doesn't address how you get to that position in the first place. What might have been true 10 or 20 years ago doesn't really fit into todays common practices or even more importantly, tomorrows.
Cadet schemes, attract a lot of good applicants. They look for individuals who are likely to do well on them. They are extremely competitive, and even for the successful few, they are often extremely expensive.
Once reality sets in, you will quickly discover that it isn't easy or quick. In your particular circumstances, you have issues that you need to consider, putting aside any such notions. You know this, and I suspect you also know that there is no tailored answer that will satisfy your questions. General research will provide all of the answers to the questions you are asking, and they are readily available.
Provided that you meet the medical standards, and you have the ability, determination and luck that are requisite vital ingredients, then there is no reason why you should be at any lesser or greater advantage than many other people who every year attempt to embark on this particular career spectrum. However there are obvious issues you need to address, and it would be pointless and wrong to suggest that these things either don't matter or wouldn't put you at a significant disadvantage if you chose not to address them.