I'm the supervisor of a seminar.
A team of two students is preparing a common presentation for the seminar. The team has to write a report (a preliminary version for double-blind reviewing by other teams and a final version read by me) and give two talks; the team has a lot of freedom on how and what they do. The topic, the seminar dates, the duration, and the deadlines for handing in the reports and the slides are fixed.
I put the two together a few months ago (they had not known each other before, so I had to do all the organization via e-mail). They already submitted the preliminary version of the report more-or-less in time. However, 5 days before handling in the final report and 12 days before the presentation, one of them complained about the poor performance of another one. I asked them to clearly state their contributions by a particular deadline; one did so, while the other did not answer by the deadline. I offered them to split and am waiting for the answer.
I do care that all the participants of the seminar and me learn something new from the students' presentations. Moreover, I get evaluated by the seminar participants anonymously; the evaluation goes to the department. I do care about good evaluation results, too.
How should I deal with such an unpleasant situation?