After some tinkering, I've found a makeshift way of doing this. VBA-M works as a controller on the same computer or over a LAN connection, but not when an external IP is used in Joybus. I realized that using Hamachi in order to connect another computer's VBA controller to the host's game actually works the same as connecting one over an ordinary LAN connection. Then, in order for the other person to see the screen, I can set up a livestream video. It "works" - the controllers are in the proper state, both inputs work, and both people can see the same screen.
However, alongside a few seconds of video delay in the livestream - which could be bearable - the link slowdown is the main issue with this method. If used on the same computer, the VBA-Dolphin connection slows FFCC to about 56% speed, and that's only if Turbo Boost is on for the VBA. If used over any form of LAN, which includes Hamachi, it slows it down to 2-3% speed. I tried changing CPU priorities, but it didn't affect performance at all; is there anything else I may be able to try?
However, alongside a few seconds of video delay in the livestream - which could be bearable - the link slowdown is the main issue with this method. If used on the same computer, the VBA-Dolphin connection slows FFCC to about 56% speed, and that's only if Turbo Boost is on for the VBA. If used over any form of LAN, which includes Hamachi, it slows it down to 2-3% speed. I tried changing CPU priorities, but it didn't affect performance at all; is there anything else I may be able to try?