Thanks for your replies, they do mean a lot.

I agree with an approach of self preservation, however, I have a SS14 whom we are both close and he would be devasted if I changed the locks and asked DW and SD to live elsewhere.  I woul'd want to do that to him or to my DW for that matter.  I feel it easier to move myself.  The whole thing is taking its's toll on my somewhat fragile mental health.  I'm sure some would argue that alone should be the deciding factor to leave, but I find myself very conflicted.  So here's my confliction:

After my walk yesterday, I went home to a very forsty and harsh atomsphere, it was clear that I was being given the entire blame for the situation.  My DW and I are undergoing some minimal talking therapies anyway and I was told that she didn't anything to say to me and that we should wait until our next therapy session on Tuesday!  I also found the SD and DW acting as though nothing had happened and we about to start online shopping.  There never seems to be any consequence for SD, again DW picking her battles and automatically leap on the defence of the SD.  I genuinely believe DW believes I'm out to attack SD.  As I've assured them both countless times, I don't wake up thinking today I shall make SD life difficult, I purely react to each situation as it happens, the difficulty for me has been to learn to leave things alone, no matter how large they are.  

I've asked my DW perviously if she wants me to leave, or to separate for a while.  I never get a straight answer, just bounced right back at me with "well if that's what you want, you choose".  Then as the months pass, it comes out in therapy that it was me that wanted to leave, it was mea that wanted to end the marriage.  All the time ignoring or not seeing the huge fact that it wasn't entered into lightly, I didn't just think one morning 'ah sod it, I'm ending this'.  I genuinely don't want to end the marriage, but I know through DW stubborness she will make final and finite.  I don't want that, I love her, just the situation is too much.  I ask myself if I can hold on until she leaves home, no idea when that will be, she's 18 in December and thinks she is totally independant.  It could be 5 years before she leaves home.  I have seen what family life can be like when SD is away, as she visited friends in Cornwall for a week recenly and family life was calm, peaceful and worthwhile.  Then the eggshells reappeared when she gets home.

It's a public holiday here in the UK this weekend, so three days at home in an envrionment I can't stand.  I'm thinking of checking into a hotel for a night or two to be out of the way and allow my mental health to calm down a little.  But, and this is the conflict.  If I do that, DW will be treat that as fixed and that I don't want to be marrried to her.  I get that's probably her anger talking, but I was and have been hoping for a response along the lines, 'ok, lets talk'  rather than 'ok, off you go'.  I don't believe she means that, just her defecence mechanisms screaming out.

I'm at a total loss and at my wits end with it all,

Thanks again everyone.

My Wife and I sat and talked yesterday.  Once again the reasons why SD is rude and hostile towards me is largely of my creation.  It's my parenting style that SD doesn't like and the two of us so alike that we clash.  For example SD gets aggressive and throws an outburst at me I react in similar way to end the situation.  Much the same way that I was patented as a kid.  My parents would not allow me or my brothers to talk to them with contempt or disrespect and so gave us a bollocking and ended the matter. We didn't need reasons and so on.  We just knew we'd over stepped the mark by their reactions.

Here, I'm not allowed to react like that.  I'm not allowed to shut down disrespect aimed at me in my own way as it's deemed wrong by my Wife.  Instead I have to remain calm and using talking therapies to understand why SD was driven to the outburst.  
 

I was told that I don't care as I don't even ask about SD health appointments.  True, I don't ask.  Mostly because I've disengaged and then because there are so many of them and I'm not told of them.  They're just put on a calendar in the kitchen and I'm told where the dates are on the calendar!  Maybe I'm in the wrong for not knowing from the calendar.

Truth of the matter is it that I have not liked the SD or SS as she/he was back then.  I find her highly selfish and utterly self centred, to an extent that I have never encountered before.  Her sense of entitlement knows no bounds were as I've always been taught to earn what you want.  A good work ethic so to speak.  sad can't even get up and get washed until 3pm and then takes 2 hours in the only bathroom before she leaves the house to hang around in a park with friends.

I get that some of that is modern teenagers but even so, to me it's highly alien and feels wrong.  After all she's 17, study travel and tourism at college and I believe wants to be cabin crew for an airline.  I ask my Wife (can't talk to SD as my emotions can better the of me when she grunts at me is answer). How can she become cabin crew and smile and greet people on to a plane when she can't even hold a conversation with those around her unless through her bloody phone?  How is she going to get up for a 4:30am flight when she can't even get out of bed before 3pm?

My point is that I see our role as parents to guide and nurture  her through that learning so she's ready.  Instead my Wife simply says but she's safe there in her room.  No one is bullying her or at least she comes out of the room though.  Agreed she does, but that to me is not normal life that she is about to enter and we're not preparing her.  Then I'm met with so why change her just because it's my perceptions of what normal should be?  
This is where the uncontrollable feeling starts in my of shear confusion.  How can I compete with that.  One minute I don't care, the next I try to demonstrate my care but getting SD up and beginning to learn life skills and then I'm told it's me and my perception rather than SD doing anything wrong.

An extension of that was that when SD does come down stairs she slumps into the living room in front of the TV.  She's helped herself to a dining room chair and uses it as foot stool and then lays out across it completely flat and covers herself with blankets (even in the summer).  I can no longer ask SD to sit up and put the chair back as I'm met with an outburst of why does matter how she's sits?  So I ask my Wife as that's the direction it seems to be going.  She says but what does it matter, at least she out of the bedroom.

It feels like I'm expected to care but then we I do it's not in the right way and I'm shut down.

I write this on the sofa, family are asleep upstairs as cry my self senseless wishing I had some rope to hand.  Had enough.