Hi Matthew - this is the sort of Q where I usually say "ignore the statutory duties and go back to first principles of common law".
So the question to be asked is "Who is your neighbour?" applying the judgment in Donoghue v Stevenson 1932 - you might have fotgotten the names but you might remember the story of the snail at the bottom of a bottle of "ginger" - which probably meant lemonade.
So, if what you ask this person to do could result in harm to them, they are your "neighbour".
Equally, if what they do for you could result in harm to someone else, that someone else is ALSO your "neighbour".
Your duty of care to your neighbour is to do what is reasonable to protect their health and safety - not vastly different to the duty to do what is "reasonably practicable" under legislation.
Doesn't actually matter what this person is doing, but since this is a health and safety discussion forum, let's use a possible H&S unpaid job to help with the person's training.
Imagine you ask them to review a COSHH assessment, remotely from home.
That they live in a hovel with a rat-infested kitchen is, frankly, none of your business as their notional employer - if you want to get them rehoused from a sense of philanthropy, so be it, but the kitchen beyond the scope of your duty to your "neighbour" - UNLESS you provide the housing.
As is what they do when playing video games and not adopting ergonomically sensible postures - UNLESS they are doing those video games as part of the training you ask them to do.
However, reviewing the COSHH assessment is within scope and probably requires this person to use some form of display screen equipment - so your duty of care DOES mean doing what is reasonable to make sure that the workstation is set up appropriately for this person to be able to work safely and some level of supervision - asking the right QQ, possibly getting photos of the set up - but NOT standing over this person 24/7.
However, if the person gets the review of the COSHH assessment horrendously wrong, this could place others at unreasonable risk - they are your "neighbours" whether your employees or not - so your duty of care extends to taking reasonable steps to check that the review is adequately done.
Then finally you can bring criminal law back to the table. If you are not doing what is reasonable to protect all your "neighbours" there will be some statutory requirement that you are breaching.
But doing what is reasonable to protect these "neighbours" isn't usually particularly onerous, particularly in the sort of scenario you present.