very quick point re sciences
you can apparently do OU courses even if you are not yet 18. I understand that several HErs have done this.
The entry level science course, S104, is great. I do not see ANY reason why a motivated gcse level student shouldn't do it, and do well, though technically its A level standard plus. The important thing is that the explanations are very, very clear, and it is designed for independent learners. There are also experiments.
Another option with the OU is their short level 1 courses, some of which are designed to teach study skills as much as science. I have done a few, they vary widely in their difficulty tbh, but the advisors are very helpful with regard to which course you should do and the website has feedback from previous students.
There is no way round it, if your child wants to do a highly academic course at university, say medicine, they MIGHT need actual A levels (though its worth talking to the uni-I know that some have accepted OU courses, including the course I mention above). But I think with anything else there would be more flexibility.
There are always options with HEing. Sometimes you have to jump through hoops, because that is life. But I think its generally best to jump through as few hoops as possible.