Speaking personally (and that's all advice ever is really, just one person's opinion), I would say that you've taken the correct first step in preventing either of them from hosting - and, perhaps equally important, avoided the misstep of allowing yourself to be drawn into siding with one or the other.
I suppose it rather boils down to what the dispute is over. For example, if one of them has moved in with the husband of the other, that might be irretrievable for the foreseeable future - but if the dispute is over something minor then perhaps it is about time that somebody told them both to grow up?
If they cannot manage to be civil to each other, then, from what you say, you're just going to have to remove both of them from the group - because you can't do otherwise without taking sides. But if you decide to do this, it needs to be a decision made by the group and communicated by the group in such a way that it's clear that the group is not expressing an opinion on either party by doing this but simply don't want to get pulled into things - just as the surgeon will cut off the gangrenous leg before the infection spreads to the rest of the body.
Do hope this is of some help - has anyone reading this been in a similar situation to this in their group? If so, how did you handle it?