Inspired by this question.
Can lepers form a Minyan, or is that an inherent contradiction in the status of a Metzora'?
I think that the answer is yes.
I base my answer on Mishnah N'ga`im 13:12:
(Informal translation: If [the leper] goes into the synagogue, they make him a barrier [mechitza] ten handbreadths high by four cubits wide. He enters first, and leaves last.)
The commentaries I've seen indicate that the problem is that if the leper is in the same room as someone, he transmits tum'ah (ritual impurity) to the other person.
(So far, BTW, all I've written applies equally to men and women; the Mishnah usually uses the male form for gender-neutral laws.)
In any case, there is no problem, according to this Mishnah, for lepers to be in the synagogue at the same time as other people. I don't think it is a stretch to say that the purpose of entering the synagogue is to pray with the congregation.
Because of other minyan considerations, all members must be present in the same space. So I don't think that lepers and non-lepers can combine to form a minyan, at least not an indoors minyan.
The Mishna seems to say that lepers can pray together with a pre-existing minyan, in shul. Therefore, their isolation doesn't have to be total. That's why I assume they can make their own minyan.