It looks to me this quest is intended to be taken at around the middle of the game, like when you are forced to go and talk to Johanka while following the main quest line.
In my case i cant finish this quest with the best results because i cant “Get better conditions for the wounded”, when i took this quest, very very early, before killing Runt, i was unable to enter the custodian house, it was locked all day, then i cured 2 pacients, the custodian showed up, i failed the dialogue check and it send me to prison for a day. I was still unable to enter his house and talk to him, so i cured the other pacients and put the quest on hold on “Tell Johanka you cant do anything more”, so i moved on the badint killing activity, i heard thats was an alternative way of getting access to his house, it did the trick, BUT i cant talk the sebastian about the wounded, after talking about the bandit killing i cant talk to him, i cant attack him and is invulnerable to poison as well, and o can petty much do nothing. I moved the main quest forward to the pestilence, that is related to Johanka, but that did nothing.