Talk:Break Manson and Franc out of prison.
You can also get the key by buying it from a super mutant. I bartered with the first guard and the key was in it's inventory, costing 0$.
I talked to Manson and Franc without opening their cells and choosed the "mutant-friendly" dialogue options without freeing them. However, it allowed me to tell Marcus Jacob and Aileen asked me to break them out of jail, even if I didn't talk to Jacob and Aileen at all.