Shikabane Hime: Kuro 8

So I'm finally all caught up on this series. :D
So far it's been great but I don't like this twist that Ouri's mom was a Corpse. And that one Shichisei is his brother. :?
They just pulled that out of nowhere it seems. I knew Ouri's childhood before being found by Keisei was a mystery for a reason but this is stupid.
Why does this Shichisei guy wait until now to bring it up?
And everyone seemed to already know in Kougon but they let Ouri be a priest anyway. :?

Of course, they haven't shown the whole story yet so maybe they can redeem it somehow.
So I'll be waiting for the next ep before declaring bullshit on this turn of events.