Lemisscared
You have lots of skills and experience, though it is a bit of a jumble.
Put a paragraph at the top about what you do and what you want to do. EG:
Science graduate with administrative skills is seeking permanent part time role....
xxx date to present
DH building company name
Assist family business with administration, tax returns, bookkeeping and invoicing. This role is part time and fits in with school hours.
Then work backwards with your employment using the same format.
You can go to an employment agency, they will test you on word, excel etc and will tell you what you need to brush up on. Adecco has an excellent testing system and can also send you online training to do. They will also give you advise about your cv and how best to get a job in your local area. Though do have at least a draft of your cv with you when you go in.
Lots of local schools and colleges will run adult computing classes too, either free or at very reasonable costs.
I have known some health charities want admin staff who have scientific backgrounds so they will have an understanding of the work they are doing. Worth looking out for those jobs.
Yes, companies do consider being a treasurer a valuable skill and deff worth putting on your cv.