The first opportunity to cite a source with more than 3 authors requires you to mention all the authors and then, subsequent to that, you may use only the first name followed by et al.
In-text: Bruwer, Prince and Victor (2010) states… or at the end of sentence... Study guides should be written in the correct format. (Bruwer Wright and Victor., 2010).
In-text subsequent to the first citation: Bruwer et al. (2010) states … or at the end of the sentence … Study guides should be written in the correct format (Bruwer et al, 2020).
Reference list: Bruwer, A., Wright, P.R., Prince, M.C. & Victor, A. (2010). The how-to guide to writing a study guide. Johannesburg: Academic Solutions Group.