Get the Lord to pick up a weapon and fight.
Despite his apparent 'weakness', he is simply superb at killing guards. Have him hold position when he gets out and then bait the first few guards over to him. Make sure to keep whacking the guards with the stick whilst the Lord strikes them down (if the Lord takes a single hit he will go back to jail!). When the first guards are down, pick up their weapons and kill the rest yourself (or let the Lord kill them again).
Pretty easy really. The difficult part is killing the Prison Guard (especially if he's a Swadian). The main strategy is: kick the guard, smack his head with the stick, kick him again, smack him again... Keep doing it until he drops (hopefully you haven't been slashed by the other guards) and run into the dungeon as soon as possible.
If you fail to sneak in successfully then I'm afraid you're going to be stuck in jail!
I wish they'd let your companions help you though. Bunduk and Katrin would put up a great fight.
If you're not at war then it's really easy. A siege crossbow will eliminate the prison guard in one hit.