How does one configure the router for load balancing upload only?

I have a VM 20mb and Plusnet 20mb which id like to make the most out of for streaming emby/video over the internet.

Has anyone got experience of this?

You would have to configure each gateway on the remote device to do this.

Accessing each IP address over the internet at the source. If this was going through a capable router, then you may be able to do this.

If you are specifically accessing on a tablet for example, then the software would need to be smart, and configurable for this. 20 meg should see you sufficient for one gateway any IMO.