Indirect connection, wont play media from a shared server

I've been sharing my server with friends and family for a few years now without a problem. For some reason recently my parents have been unable to connect with my server.
I have deleted off the app on their ipad, sent a new invite, reinstalled everything including the Chromecast dongle. So now I have the Plex sever installed on their wired PC and the app on their ipad. On the PC I can now finally see my sever, but it says 'Indirect Connection'. I can see all my media files but none of them will play.
I have done a search for Indirect connection in the help section but nothing comes up. I have no problem with the one 6 people who share my library so I know the problem is not at my PC end, it must be this end, maybe with access through the Sky router?
Any help with this gratefully received as nothing I have tried seems to work.