I guess it's a trickier questline for people than I thought. I think it's best to rescue those as one of the first things You do in Act 2. I got this thing done the first time I tried, even with encountering some bugs and nuisances, so I will write for You how I did it below:
After You enter Towers You can get straight to the small closed doors on the right side of the hall. Stop here, close all the doors and wait for the Warden Eye, then kill it fast. This eye goes down to the prison so You have minus one already. Then go down and here You meet two guard ladies and a cultist on duty. You can leave them alive if You want, they are unimportant for the rescue mission if You do it right.
Next, go to the torture chamber opposite the guarding ladies, close the door and wait for the Warden Eye, kill it fast. Here it got tricky for me, as it appears there were two invisible investigators in the room. I've talked myself out and positioned my team for 2vs1 fight each. Be sure to kill them or out them fast, so they will not alarm anyone in the Towers.
Then You can go further. I checked how the prison looked and how many guards were there. Then I entered the Warden's Tower in the center. Remember to close the door before anything! You can talk with the Warden etc. I did, then I somehow missclicked or there was some bug, I don't remember, but one of my characters used the ladder to go up. This place was off-limits so the Warden also got on the upper floor to talk with my poor companion. Up there is the Eye, so this was my first target, and then I attacked the Warden after the talk. Other characters blocked her path to the ladder so she couldn't get to the levers; to be fair I did it by accident, never thought she would otherwise focus the levers. While fighting with her here You'll have to remember that there is a second Eye that can enter that tower through closed doors on the lower floor, so watch for it or prepare a companion to kill it quickly when it does so and I suggest You to kill that second Eye here when it enters.
After this You have all that tower for yourself, no one suspecting anything. Then from the upper floor go to the wooden balcony and from here You have a view of most of the prison and cells. Remember to stay hidden, thanks to this You will see all of the guard's line of sight. What is left are two guards and one Eye. Use the turn mode and firstly focus on the Eye! Wait until it is in shooting range, but not in the line of sight of the static guard at the end of the prison. I had two rogues here so they sneak attacked from here. After You kill the Eye, the patrolling guard will come to the place where it was destroyed and shout about murder... Just shoot or sneak attack her also!
Then You can get out of Warden's Tower and go to the last guard who unfortunately for him was too nearsighted and didn't realize what I did in front of his eyes. You can just kill the poor guy on the spot.
I'm kind of an explorer so after this and before I made the next move and freed prisoners I checked all of the prison for an eventual alternative way out and since I don't want to spoil things too much for You I just suggest it to You also. Remember that You can move boxes and chests around and also use them in creative ways such as stairs or something! Hope it helps.
