DID IT! .. though it feels like cheating since i used setstage :/
soo there are 2 ways you can do this ..
First: The way of some killing/content/ammunition(and a goodie):
1.open console
2. type in:"player.moveto 0010FA76" to get into the Safehouse and get the Objective "kill all courser"
3. Unfortunately after that you have to go outside so from this point out you have to use setstage to progress
4.type in:"player.setstage RR301 300" -> this will finish "kill all courser" objective and tell you to talk to Desdemona
Second: The fast way without the fun:
1. open console
2.type in: "player.setstage RR301 0" or "player.setstage RR301 50" (i think its 50 but i havent comfirmed this since im already past this point and screwed up with my saves :/)
3.type in: "player.setstage RR301 300" -> this will again finish the "kill all courser" objective and tell you to talk to Desdemona
i hope i did atleast some things right with formating .. maybe you could clean up this mess and make it presentable^^