There are lots of chairs on the Liberty, but your best chance at finding six together will be in the areas away from the pools. The chair hogs seem to congregate around the pool, with their little tokens marking chairs as theirs for the whole day. The RCI pool staff is often efficient at policing it. I've seen them wait a bit (maybe 30 minutes) and if nobody appears at the phantom shoe or book left on a chair, they will remove it. The only chairs reserved are those for suite guests, and they will have a roped off area with someone checking cruise cards. Don't try to tip someone to guard chairs for you. They are not allowed to do that, and if caught they could be fired.
But if you go up one deck and then go forward you will find several little out of the way areas with available chairs. Nothing says you can't move empty chairs together if they are spread out. Bar waiters come by and it is quieter. However wind can sometimes be an issue.