I can't for my life find out why this doesn't work (I'm a newbie).

If I use my Macbook Pro laptop or Samsung Galaxy S5, I CAN'T find the Chromecast, when I go into the Google Cast app and look for devices.

However, I CAN still stream content to the Chromecast.

But if I try to stream from a Samsung Galaxy tablet, I CAN'T stream (this is particular important, as this is the only device, which my mother in law can use to stream for example Netflix to the TV.

I've restarted the router several times, I've pulled Chromecast out of the TV and restarted it.

I've even gone in to the router settings and set the channel to a certain one (and not just let it choose an automatic number).

Then I've read elsewhere that someone else is having the same issues with the same router (Thomson TG585 v8 router).
https://productforums.google.com/forum/#!topic/chromecast/11iSR0Xl_QQ

Apparently I need to disable the 'AP isolation', but there's no such option to do this, when I log into the router.

I'm starting to believe that I have to buy another router for my mother in law. Although that I can stream from the Macbook Pro or the Galaxy S5, it's still a bit weird that neither of the devices says that they can find the actual Chromecast.

Surely that can't true though...

Any help is much appreciated.