Wireless repeater and bridge

I have compiled openwrt with relayd on my lattepanda that could connect ethernet only devices to my wifi.

I have a new scenario I need to setup.
Lattepanda has

I need one wifi card (card a) to connect to a another hotspot
I need one wifi card (card b) to act as another hotspot, connecting it to the other wifi card
I need the gbe (card c) to connect to card b

The intention is this
My mobile hotspot has internet, however it's not always on. I have several servers like plex running on my NAS that my nvidia shield needs access to. I need to connect my shield to the lattepanda permanently through wifi. I need that wifi hotspot to treat the ethernet port as just another client. I then need to provide internet access to the hotspot by connecting the other wifi card to my mobile hotspot.

Sorry if this is confusing. I just need an always on wifi hotspot that will auto connect to my phone to provide internet.

Is this possible? I haven't messed with networking in a while, I just remember relayd is what got my ethernet only device to connect to wifi.