If you are citing multiple sources in the same reference, you should list them in alphabetical order separated by a semi colon.
(Adam et al., 2018; Carpenter et al., 2015; Zepke, 2017)
If you want to give emphasis to some authors over other authors, separate the sources so that the emphasised source/s appear first and the remainder follow the words ‘see also’.
(Giddens, 1991; see also Archer, 2003, 2007)
If you are citing multiple works by the same author published in different years at the same point in your text, you should list the author’s last name followed by the relevant years of publication.
(Archer, 2003, 2007, 2012)
When citing information from multiple pages within the same source, you should cite consecutive pages (i.e. 2 or more pages in a row) with pp. followed by the page number range.
Zepke (2017, pp. 55-56)
For information from non-consecutive pages list each page number separated by a comma.
Zepke (2017, pp. 14, 55, 102)