can you not employ on a commission basis like taxi companys do with employees. one man should be bringing around £200 + a day, where r u based
talk to them and let them know you are not happy with there takings on a daily basis, put them on part time, I in a van, they seem to be happy working to geather having a laugh etc, extended breaks etc.
start working with one of them, see what there routine is. see how much you bring in when you are working with them