Access my Media server offsite / away from home?

Hi all
I have a Synology DS 412+ and a WD TV Life.
My aim to provide the WD TV Live to my in laws with the intention of them being able to access my DS412+ from their home over the internet.
They would use it mostly for movies and music.
I’m struggling to find any details on how to do this however.

Can anyone help?



The WD TV does not have an option to specify a remote DNLA server configuration.