Integration Services License requirements Not sure this is something which people will know on here are not.  

We currently have a BI setup where we have Integration services on one SQL instance and the data warehouse database on a separate SQL Instance.  

My question is, as no users physically connect to the Integration services SQL instance and it is purely used to execute package from the integrations service catalog via SQL agent, do we need to License every user i.e. Cal's for that SQL instance.

Basically i'm wanting to know if I could utilize SQL 2016 for an integration services instance and use features like Json manipulation etc and then load this data into the 2014 version instance...but what level of licensing will I need?
If users are not accessing the 2016 Instance itself, there's no need to licence them for CALs to it, just need a licence for itself for production purposes - Server or (in this case, avoid) Core. 

It is unusual that you would use a Server licence without CALs, Microsoft would probably be interested on an audit... but as you note, your users are on 2014 CALs accessing their 2014 Server Instance, so would be covered for that (assuming no pass-through or multiplexing going on). However, as at least one user will need to use SSMS or VS etc to manage the 2016 SSIS packages or indeed server, I'd suggest a 2016 CAL for them.

Disclaimer: I'm a Microsoft Licensing Sales Specialist and sell MS Licencing online in UK, any advice may be given freely but ultimate responsibility is of the licencee.