Biscuits, my daughter already took two GCSEs this summer, in Maths and English. With home ed you don't need to stick to the usual school timetable of taking 8 to 10 GCSEs all at once. She's now considering whether to take another year at home and do another couple of GCSEs, or go to a local college where they take home ed students aged 14 to 16, to do a BTEC diploma. I hope she takes the college route as I can't see the advantage in having the extra GCSEs, and I think she is ready for the challenge of college now (she'll be 15 by the time she starts).
I don't personally teach, maths, languages, science, humanities, etc, no - but I don't need to be able to. Each of my children are different, but taking my eldest as an example, she has no interest in languages, so she hasn't studied them at all. If she needs / wants to do this when she's older, she can. We're conditioned by the school experience to believe that everyone needs to study a lot of subjects whether they interest them or not - and not go deeply into any subject, no matter how much it interests them, until they reach the 'correct' age. Home ed doesn't have to look like that.
I don't personally teach any subjects in a formal way and you might not recognise a lot of what we do as education. But my children are learning all the time and they are bright, enthusiastic, and motivated to discover all they can about their passions. It's a big topic, but you might like to read about unschooling or autonomous learning to get an idea how children can learn without a school type education.
When my children want or need to learn something I don't know enough about, we research it together (books, internet, tv) or find someone who can help them (another home ed parent, a tutor, someone local who can show them a skill), or more often, they find ways to find it out themselves and then come and show me what they've discovered. I don't know how they've learned half the things they have! It honestly amazes me. And because it's come from their own motivation to learn, they retain the information and it is meaningful to them. They don't bother learning things they don't want or need to know, so they also have plenty of time to play and relax and muck about. There is huge amounts of mucking about involved. 