I think if your going to do it , take them on as employed either full or part time , you will find that when you dont have enough work for them to do you will actually find extra work for them just to make sure they have earnt thier wage
I did this around 6 mths ago he only works 1.5 days a week but we get through a lot of work together, I dont regret taking him on 1 bit hes worth every penny