It depends on the group composition. If they’re all random players, 3 votes is enough. If a group of 3 joins together, the 4th vote is required for the kick. So a group of 3 cannot kick without a 4th in agreement.
That said, when groups join and initiate a kick, the system keeps track and if they do it frequently, they lose the ability altogether to initiate a vote even. They get out onto a cooldown until they complete some runs without any attempts to initiate a vote to kick.
It’s a sort of safeguard to prevent constantly just kicking people for funsies.