Thanks Kew, we'll all keep hoping and praying. Something of that magnitude will take its own course and time. I can't imagine what agony PC and his children must be going through .
My problems seem totally immaterial now. Suffice to say I tried the distancing strategy last night, and it paid off. No more talk of selling up, a pleasant evening spent in front of the box with DP gradually relaxing as he realised I wasn't going to raise any awkward issues. DP slept in our bed again and not on the sofa as he's said he would the night before, and we are tentatively getting back to 'normal' - whatever that is or ever will be. I have had some brilliant advice from Someone we all Know, which has shown me that DP is not being an arse for the sake of it - it is all a part of his disease. If he won't seek help for it, I must learn to ride it - and last night, I think I started my first lesson well. I've talked to DD too, so she understands that he doesn't really hate her, he's just using her as a focus for his own inner pain and confusion.
I feel so much more empowered now, think I can face things better now and love DP for the person he is, without indulging his behaviour or encouraging it by rising to it. Thanks to all for your support.
But heck, what we all really want, is for PC's bro to pull through! Big hugs to her.