How to deal with co-PhD student demanding too much time? Me and another PhD student have the same schedule. However, they are not pulling their weight and I feel as if I have to do far more than necessary to compensate -- I have to do research, read papers and explain them to them, give presentations, do their work, and have long meetings with them to discuss things that I already know. They read only papers that I specifically recommend, and so are bringing no knowledge/ideas/viewpoints I don't already have. They constantly interrupt me while working and act extremely entitled to (large amounts of) my time. We're at the same point in our PhDs.

They are rude and I don't wish to invest a significant amount of energy teaching them how to be a functioning member of the department. I have already tried teaching them how to find papers to read and research avenues to pursue independently, and how to manage their time so that I don't need to do the work of the 'group' entirely by myself every time. It hasn't worked. At best, they will go and ask someone else to explain whatever topic I've asked them to learn about, and then we're on the same level again. 

We are involved in research projects together (without anyone else to notice this behaviour) and I do not wish to abandon the projects. We are also required to take classes together with the same goal (to prompt/produce research projects) next semester, and so I want to know how best to handle this before this repeats itself.

We have to work with one another closely for the next 2 years so I don't want to burn bridges, but I was wondering whether it'd be within reason to tell my supervisor, or whether I should just take action to avoid this person and not burden myself with them as 'co-researcher' or co-TA ever again? I close my office door and let the student know that this means don't interrupt, but this has not been respected. I definitely don't want to isolate myself from the rest of the group but at this point I don't really know what to do except work from home.
You need to enforce your boundaries better. I understand this isn't always easy to do, emotionally. But "no" really can be a complete sentence. Or "not now, I'm busy." This person has no authority over you, so if they don't respect your "don't interrupt me when my door is closed" policy, stop opening the door for them.