According to the plan that Harley had, they would have to split into groups on their way to the fortress.
With a smaller group, it will be easier to move, manage everyone, and avoid attracting attention from their enemies. If one of them gets captured, the others will still be there to help them out - unlike if they are to gather together and end up getting all of them caught.
That being said, Zen stays with his usual companions and two other new members, Harley and Dennard. The other groups will take an easier and safer route than them since they have the most number of skilled fighters. They are still using the campervan that they have gotten their hands on, which fortunately remains undiscovered by the invaders and spies who infiltrated the hideout. Their comrades have used their respective vehicles as well.
Everyone needs to meet up again at one particular location near the fortress after a month of travel.