For second and subsequent citations, cite the surname for the first two authors, and of as many as the next authors as necessary to differentiate the two works, followed by a comma and et al.
For example:
(Smith & Croft et al., 2010)
(Smith & Atkins et al., 2010)
(Cranston, Bell, Lewis, et al., 2014)
(Cranston, Bell, Allen, et al., 2014)