DLNA, Hotspot and two WiFi networks

Afternoon all.
I’m using OSMC as the setup for my headrest monitors for my children. I’d really like some help if possible, please. My eldest son is always on his phone watching youtube videos, I’ve figured out how to screen mirror using DLNA, (I think)… but if possible I’d like to use the built-in the wifi to connect to my home wifi, (so that I can continue to use the SMB shares to add content) but have a USB wifi adapter act as a wireless hotspot that can be used to connect to the pi. the problem I can see is that when a phone is connected to the pi as a hotspot it expects to be able to reach the internet through that hotspot.

I’m happy to use SSH to install the packages needed, but *nix is a relatively unexplored territory for me. (I’m an IT manager in a windows world)

Any help is much appreciated.