The OU degree is a good route - whilst less mainstream, the OU is highly regarded, and the whole system is designed for people like you who have commitments but a desire to progress in new directions that need academic qualifications. If you pick the right options (mostly mechanical ones), their BEng(Hons) will qualify you to go for Incorporated Engineer, and with the addition later of an MSc you could go for CEng.
There's a significant interchangeability between Aeronautical and Mechanical Engineering - plenty of people with MechEng degrees are working in aeronautics, and for what it's worth my degrees are in Aeronautical Engineering, and I managed to also become a Chartered Mechanical Engineer off the back of that.
Before you can progress with it, you're going to need much better maths and physics. There are two obvious ways to do this - either one of the OU's "access to..." courses that they offer for exactly this sort of purpose, and the other is go to a local college and do these by evening classes - there are various options there that'll get you first year degree entry: HNC, BTEC, A-levels, but if you are absolutely set on a degree, then I'd recommend the last, as they're specifically designed as university entry qualifications and will set you up best for degree level study.
In the long run, the chaps above are right that you're likely to have to move for jobs once you have your degree -we've all been up against that: obvious centres of graduate aero-eng jobs are around Bristol, Preston, Derby, bits of Hampshire and Wiltshire, Cambridge - but it can be possible to be reasonably settled once you've made that move. But with the OU route, you can put that off for a few years.
Good luck,
G