Every single time I try to do this mission when I go to stealth knock out the guards, one of the two is always notified no matter what. My noise is at zero and they shouldn’t know I am behind them it’s driving me fricking nuts.
Check the quest bug here https://www.reddit.com/r/kingdomcome/comments/80t790/a_list_of_all_of_the_broken_quests_in_the_game/
I think its not possible to be stealthy in this mission
I did it after trying 30 times. Make sure you save right before you walk up to them.
I felt like standing super close to them helps, and not just when the stealth attack prompts.
Try and try and try, and in the end it will work… at least it did for me
Spoiler alert but you fail this mission anyway, there is no way of completing it successfully. Your best bet is to let the first guards see you and raise the alarm and then escape with Hans. This quest is full of bugs
Knock out rather than kill the first one, it’s stealthier. You can always stick him later.