Crew Strategies for Dealing with Roving Impostor Team

In my local playgroup, the stronger players have figured out that when they're impostors, they can be super effective by traveling together as a team – getting double kills, making people feel safe (as they think if one is an impostor, the other will be a potential witness if they're murdered), coordinating sabotage, and acting as alibis for one another in discussions whenever a body is found (or when they self-report).

What are the effective ways for crewmates to counter the strategy of impostors roving together as a team? The only obvious thing to come to mind is that crew have to clump together in big clusters, but I feel that will really slow the game down (tasks will take forever to complete) and requires a level of metagame pre-coordination that might "break" the game.

The other obvious answer is "see how the stronger players respond to the strategy when it's used against them," but I fear the weaker players in my group aren't going to be able to muster the strong "roving impostor team" strategy effectively enough to require a stronger team to develop a defense – meaning I need outside insight and input to help me arm the weaker players, lest they fall victim to steamrolls endlessly.

Any ideas?