Three to Five Authors
When a source has three, four, or five authors, it is important to use all the names in the first citation. This properly credits all the source contributors. List the authors in the order that they appear in the byline of the original source. This order was predetermined by the authors prior to publication. After the first citation, list only the surname of the first author followed by the phrase et al. to replace the remaining authors. The phrase is not italicized, but there is always a period at the end of the phrase.
Six or More Authors
When a source has six or more authors, listing them all can be cumbersome. In this case, the surname of the first author is always used with the phrase et al.
If you need to cite multiple sources that include authors of the same name, and the same publication year, list the surname of the first authors and as many of the remaining authors until the citations become distinguishable from each other.
[Source: APA Manual, 6th Edition, section 6.2]