First, if you GoPro support WDS you can configure the repeater as WDS, so that you don’t have a 192.168.8 subnet at all. All devices is connected to GoPro. But I believe there is no WDS for GoPro because it is not router and the wifi should be very simple AP.

But I think in order to communicate with 8554 and 80 port of GoPro from your LAN devices, it should just work. Like http://10.5.5.9/ should be your GoPro. For UDP 8554 should be the same. If the request is initiated from your LAN devices, GoPro is like a server running on the Internet there is no blocks.

If for some reason, GoPro need some extra port so that it can communicate back the to LAN devices, the data maybe blocked by the firewall.