If they earn under £95 per week your don't need to do anything!
I would check that with your accountant if I were you.
They can't possibly be only earning less than £95 per week in total and so the inland revenue need to know about everything they earn to assess their liabilities.
Even if they are on benefits, they will need to know in case it affects what they receive.
If it turns out that they should have been paying some tax, guess who will be responsible for paying it... you my friend... happened to a colleague of mine.