Endnote X8 citations for 2 or more authors

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Hi,

I am using Endnote X8 with a style based on Harvard. For my thesis I need to adhere to the following:

"Where there are 2 authors, both should appear in brackets. For example:

A more recent study (Pooke and Newall, 2007) disproved the earlier findings.

I f there are 3 or more authors, only the first should appear, followed by the term “et al.” "

I’ve tried everything I can think of in the Citation Template/Author list etc with no luck. 

Can anyone help?

Thanks