I've already answered how to unlock the doctor, if you scroll through the comments on the Itchio page you should be able to find my response.
I probably won't make a full guide because there are too many endings (and I am working on too many other things), but each girl has 2 endings, a good and a bad end, which you unlock by talking to them 4 times and raising enough money to pay your rent by the deadline. The good and bad ends are determined by the choices you make talking to them, and if you're consistently nice or consistently mean.
There's also a bunch of other shorter bad endings which make up the rest (eg letting your stress get too high, letting your thirst get too high, not being able to pay your rent on time, and then a bunch of permutations on these mostly based on your affection with sumire and juriel. several of the generic bad ends have alternate versions if you're at max relationship w/ sumire or juriel specifically).