I've been on an instrumental hiatus from music for 2 years due to my GCSE exams and from singing for a year. I've been told I can take back up 2 out of the 4 instruments I used to play and have lessons for, so I picked piano and saxophone. The issue is that my mum volunteered me for teaching a 6 year old who lives across the road music theory and piano. It's all well and good that I now have a job, but I haven't touched a piano in 2 years and haven't had a lesson in about 3-4 years, and now I have to teach it. I only reached grade 2/3 on the piano as my teacher ended up teaching me singing and theory as well, taking up much of my lesson time. I'm concerned about not being able to play well enough quickly to teach her well, plus I was terrible at practising even as a small child, and I'm worried this habit will return along with other malpractices like not cutting my nails short enough and having terrible hand posture.
The books I was taught from (which I intend to use) had accompaniments for the teacher to play along with the pupil, while not overtly complicated, I'm still worrying. Also, I have limited practise time for both instruments as my father is a noise freak and hates almost anything louder than a whisper (obviously a saxophone is a bit louder than that.) However, however the keyboard I own does allow for headphones whilst still being fully weighted. How do I quickly get back into playing in a way that can allow me to teach an absolute beginner? Also, how do I get my saxophone playing back up towards the previous standard (I was studying for grade 7) at a fast enough speed that I can finish grade 8 before university (in 2 years time)?