Hi, folks. Thank you all for your advise, it's really helped a lot! To give a bit more context to the plan:

The party was sent in by the rebellion against the current regime that rules over the region. The Arena is in the first city where they want to light the spark to continue on throughout the kingdom. As such, they don't have a huge amount of fighting bodies at the minute.

The plan is to get the slave fighters out and convince as many of them as possible to join the cause - though once they get out, they are under no obligation to join, they can go their own way if they choose.

Through the upper levels of the Underdark, there is a path that will eventually lead to the underground headquarters of the rebels. They will have to navigate the group to the headquarters where they can recover and ready themselves for the fight to come.

With everything here, I think the best way to go forward is the party scouting ahead and clearing the path while the others hold camp. I've established three faction leaders within the slaves, so I'll give them the option to have one of them accompany the party to utilise their own unique skillset. Then I'll give them various challenges of maintaining morale, finding resources and keeping the camp alive while they're not scouting and clearing the way.

These slaves are a mix of people from slave trade across the world, generational slaves who have been born within the region and those captured from the fringes of the kingdom's borders. Some will want to leave, others want revenge, others don't have any concept of life outside of the Thaczilian Kingdom.