as we are gearing up to move pretty soon (December) into a bigger place and are accepting more people in the process is being clarified, especially how we can present how it works to new comers.
we try to be quite clear on some topics such as taking part in daily and weekly tasks such as coffee making, dishes, cleaning. those are probably the only expectations at the moment.
except those, as we are young in all this, the criteria and expectations are a bit blurry, so far we stick to "gut feeling" at founders' level.
simply saying "two weeks" is not enough I agree. but we are small so I think that in 2 weeks we will get a pretty decent idea of how a person behaves in most times. I suppose something more formal, similar to yours, will come in time.
as for "Do people know why they're not being admitted?"
so far we have not faced that situation, I guess we would try to, but depending on the person and situation it might be sensitive and difficult just like you've experienced.