Americans United, Clergy Voice, and that pesky C St house

A clergy group in Ohio with a background in IRS regulations is asking questions about a certain house on C St in Washington DC:

“As we understand it, C Street Center has no recognized creed or form of worship, no distinct ecclesiastical government, and no formal code of doctrine,” observes the clergy letter. “To the best of our knowledge, it is not led by ordained ministers, and its leadership is not selected based on the completion of any prescribed studies for the preparation of ministers. We are not aware of it holding regular religious services that are open to the public, it has no Sunday schools for religious instruction of the young, and it has no distinct religious history.”

Clergy Voice asserts that the C Street Center is really a boarding house and concludes, “An organization whose chief activity is providing room and board to Members of Congress is not a church.”

I for one wish the folks at the Internal Revenue Service luck in navigating this one; as far as I can tell The Family isn't actually a Christian group, much less a Religious Right group (as AU claims here), but they're engaged in some sort of exercise in American civil religion. I'd hate to be the investigator stuck trying to make the right distinctions here.