Hello dear ladies. I have had a busy few days but it's all been nice treaty stuff, which makes a change as things have been a bit of a grind recently. We went to the Blenheim Flower Show on Sat, then a very cute village fete on Sunday which was straight out of The Vicar of Dibley. Monday was supposed to be a worky meeting in London, which has been postponed so I just had a quick night out, came home then went off on a spa break on Tuesday morning and then shopping in Bath on the way home yest. But once DP starts his new job in a couple of weeks I will have no time off and no treats, and also it reminded him that keeping the show on the road with the girls is hard, and he didn't do any of the tons of things I do alongside looking after them 
Poor, poor you, Arti. No wonder you feel strung out. I think the current arrangement is not sustainable if it is making you so unhappy, but maybe it could be made more bearable with tweaking? I think you need to look at all of the elements in your life and check whether they are GENUINELY unmovable. You say you cannot reduce hours at work (let's leave the financial element aside for a mo) - are you sure? Have you asked? Begged? Told them it's not working? Explained that they are in danger of losing you for good? Can you come up with some sort of solution that would be acceptable to them? Your current hours are extremely punishing for someone with small children.
You say you couldn't afford to cut your hours anyway - is there anything you and DH can economise on or any wiggle room with the current mortgage (go interest only for two or three years on all or part of it? It won't make much difference to the mortgage itself, you can catch up later, but could make a fantastic difference to what you pay. I did this with my flat in London in 2010. I am shortly to return to a full repayment mortgage, but it's meant that for a few years my monthly contributions were about a third less). Then the extra cash could cope with a reduction in hours if work allowed you, or to get people in to help with the jobs like you used to.
Why not get the rental value of your house assessed just to see if letting it and moving to a smaller place in the area is actually a goer. That way, it's temporary and you still get to hang on to your lovely house. I think it's all about testing the water, making small changes if you can and seeing how you feel rather than massive irreversible ones.
I do think you would find life outside London a bit of a culture shock, and I say that as one who is fairly happy here now. I would still prefer to be in town but there are lots of things I enjoy about round here and I have a good support network - and I do accept that schools-wise we are better off than we would be if we lived (say) where my flat is in London, and the green space for the girls is lovely (though I am a massive fan of London parks). Moving away from a swathe of London friends could be isolating, even though you would make other good friends in time.
As for the whole SAHM thing (and I have loved reading people's thoughts on this, girls, so thnks for sharing) as you know I am basically a SAHM with frills I am at home with the girls, but still do bits of writing and journalism and freelance editing and other similar projects for which I get a bit of dough and kudos, as well as chairing pre-school, running the cricket team and all the other things that eat my time. I just about keep my hand in and keep my ego happy with the work I do (though it is the minimum and I would like to do more), but yet get to be with the girls. However - I don't do quite enough work to be satisfying or particularly lucrative and this frustrates me at times. On the other hand, if it comes to it I have, and do, and will choose being with the girls. Whilst I recognise this, I do feel that I have sacrificed an interesting and potentially rather successful career. However, I know that as a mother whatever one does will be served with a massive great slice of 'What If' pie, a side order or frustration and if you're extra unlucky a sprinkling of guilt. As Vag has said, being a SAHM ( a privilege in many ways and a yoke in others) is no panacea. Nor even is being part time (which may be the best of the bunch). I think you need to get away with DH for a weekend, examine every element and thrash it all out.
Beans, I know your ES has the most dreadful probs with her DH but truly, her self indulgence knows no bounds! It sounds massively annoying and upsetting but at least you and your other sister were there to support your Mum. I hope it didn't wreck it for you totally. I think just ignore her for a while until your irritation has receded. I think having it out with her would just lead to more ghastly and annoying scenes.
Rubes, are you settling in a bit more? How is everything? I cannot believe how sporty your DS's school sounds, it's still with pond-dipping and nature activities etc around here...When do the kids break up and how long is this block where you are working a lot?
DB, it's lovely to see you back and it gives me a huge amount of pleasure that your DS is prospering at school. I never doubted he would but it is still wonderful to hear.
Hons, I think your girls' routine is like mine (they share a room, go to bed at the same time). But mine go to bed at 8. They have to be woken every morning but if I try sending them to bed earlier they mess around and don't sleep and also we struggle to get everything done.
Right, you must all be sick of my voice and I am knackered so I am taking myself off to bed!