You poor thing. Can you make an urgent appointment to see your GP in the morning? If you are worried you might hurt them, then things have gone too far and you need help. That said, I know exactly where you are coming from and you are neither weak nor a bad mum for hitting your limit. When you have babies screaming all day long, no matter what you do, it does bring you to a very low level.
Please also speak to your OH about it and make sure he knows you feel this bad. He may be able to get some compassionate leave from work so you have an extra pair of hands. Do you have family or any friends nearby that you can call on? I know it's very, very hard to admit you need help (I struggle with this myself) but you need a break at the moment.
In terms of practical support, I think they get harder to deal with when they are trying to crack something developmentally, and sometimes sleep goes to pot and sometimes they cry more. If they're trying to crawl then this could be a big part of it. The good news is that when they can crawl you may find them slightly less demanding in many ways.
Their bedtime is just the same as I have always used with mine, but I wonder if they could do with having naps slightly adjusted. I would try putting them down for their morning nap around 8.30-9 for 45-60 mins and then bring everything else forward accordingly, so they would go down for their lunchtime sleep more like 12.30.
Also I'm not sure whether you give them milk when they first wake (it reads as though breakfast is the first food offered) but I still give mine milk upon waking (18 months old) and maybe hunger/thirst is getting them off to a bad start in terms of mood.
I would say lunch is late at the moment, and would stick to 11.30 for a while, look at them for cues of whether they even need it a bit earlier. Otherwise snacks and meals look fine.
How much/what type of food are you giving them? Do you think there's any chance they are still hungry and that's what is making them cranky? Are they getting plenty of protein?
Also, how much milk do they drink over the course of the day? At 9 months/7 months I was giving mine 3 x 210mls (7oz) per day - timed around 7am, 2.30pm and 6pm.
I don't know if you are opposed to the idea of Gina Ford but her routines were so, so helpful to me. It doesn't mean you have to be strict about every detail (though some people read it that way), you can just follow the basic principles and tweak to suit your babies. I found it so useful to have a structure I could work around and use to support me, otherwise I think I'd have been floundering around not sure which way was up.
Do try and get yourself out of the house with them at least once a day if you can. I always found 3.15-3.30pm the best sort of time to try this, on the assumption that they'd sleep til 2.30 and then need some milk and a nappy change. If you can encourage your friends to meet for coffee at 3.30 somewhere near you this should be do-able, and you really need to have a break from your four walls.
But as I said, first step please is to speak to your OH and then your GP, and tell him/her you are finding it difficult.
Good luck and please go easy on yourself, it's a very hard job and you are doing so well xx