There’s no way of doing that live, even if you had the fastest of internet and the latency is just a fraction of a second, it’s still enough to keep every off the beat. Even if you had a click track, the latency varies, so it’s not possible for all to be in sync. They all recorded separately and then edited it together. I suspect they email the audio tracks to each other and build it like you would at a studio when artists come in separately to do their parts. Once the song is mixed and done, they all record themselves lip-synching/mimicking to the final audio track. There’s a lot going on with the synth, including finger snaps, etc. so it’s impossible to film an accurate representation. You can pretend there’s someone off camera changing the patches as the song progresses. 😉
However, it’s them playing in the recording and I’m astounded at the vocals, I’ve never heard anyone sound so close to Freddy. Freddy was so unique, it’s mind-blowing. I heard Marc Martel (doing Freddy) did the voice of Freddy for the Queen movie Bohemian Rhapsody.