To be made up of:
If there are four or more authors cite the first name listed in the source followed by et al. All authors'/editors' names would be listed in your reference, no matter how many there are, as shown below.
Research suggests (Darlow et al., 2013).
Reference List :
Darlow, B., Dowell, A., Baxter, G.D., Mathieson, F., Perry, M. and Dean, S, (2013). 'The enduring impact of what clinicians say to people with low back pain', Annals of Family Medicine, 11 (6), pp.527-534.