copying from question post.
Q: Could a team of us [British GMs] beat Magnus?
A: We stand a much better chance. I mean just in terms of spotting tactics or spotting ideas. But somebody would need to be the boss somehow with good clear idea of what needs to be done because obviously if you've got completely different people it could get confusing. But I do think that the team would have a better chance than individually - absolutely.
To add something original:
We've seen the Botez siblings team up against Eric Rosen to avoid adoption at least. See here or the 'in the hall of the mountain king' part.
Consider like one person has a particular tactical plan and then it's split into several moves that the opponent could respond with. Assign to each move to a team member. Tactically, I really don't see how you can't delegate here. Just get 1 person to do the strategy as Matthew Sadler seems to say.
Maybe related: https://chess.stackexchange.com/a/36747In Hand and Brain chess, is the stronger player generally preferred to be the hand or the brain?