I did the quest objectives by lowering the bridge and killing all the enemys. Both Mari and Son survived. I forgot speaking to them in time to get my quest reward (I was more interessted in exploring their home), and now both are gone and the quest is still open. As they are also not in their house, I assume this as a bug as I cannot close the quest now.
If you actually talk to them, they mention going to the barracks. Might check there, since in my game that's where they went.