The number of authors names option is easily modified, by editing the output style. I have done so in the attached Zip file containing a modified oikos style. Save it and make sure you have changed your manuscript to use this modified style name. The settings I altered are under Citations, Authors Lists, both the first appearance and the subsequent appearances sections.
You can find the “tutorial” to edit output styles links here for [mac](https://support.clarivate.com/Endnote/servlet/fileField?entityId=ka11K000000ONtTQAW&field=CA_Attachment_2 Body s) and [pc](https://support.clarivate.com/Endnote/servlet/fileField?entityId=ka11K000000ONtTQAW&field=CA_Attachment_1 Body s)
With respect to abbreviations, you should read and watch the video here: EndNote: Generate full or abbreviated journal names. The output style is already set to use abbreviation 1, but it will only work if you have a correct journal terms list. If you have never set it up, it is likely that the one you have, has been autogenerated by the default settings as you bring in references, and is almost always a jumbled mess. So delete and start over! And turn off the default preferences setting to auto-update the journal terms list from database entries which often end up importing the abbreviation into the “full” and the full into the “abbrev” columns. Untick the two boxes in the Terms Lists EndNote preferences. see in the attached image file.
Oikos updated.zip (1.53 KB)