Multisite Shortcode / jquery – Related Listings

Hi,

I am testing a multisite using V8.3

I have currently 3 sites, all using responsive directory theme. I will be adding more hopefully using coupon, classified & micojobs etc. so I want to use Multisite.

I have same user advertising across all three sites, currently in the author section, the “view all listings” by the author will only pull in the listings on that current site.
Can anyone assist with code what I can put in here to bring in the user’s listings in the other sites to populate either in the author box section I have in the sidebar beside their listing, OR under their listing as a “related listing”.

The reason I ask is:

I have a user, they are a hotel business. Within this hotel business they have a restaurant open to the public, a gym open to membership, a beauty salon open to the public and a bar that hold live music events.

I want them to advertise their hotel in my hotel site, their restaurant in my restaurant site and their gym, beauty salon and their live music events in my What’s On site.

When a visitor then views their hotel listing, I want at the bottom or the side this hotel’s listings for their restaurant, beauty salon, gym and live music events to show up.

I know they use different databases, but, when I am in each separate site I can easily add their username to each site using the “add an existing user” option and it just pulls it in, so it can surely be done? Maybe as related listings shortcode under would be easier than in the author box?

Thanks.