Hi Weepy, I don't have twins, so I won't presume to say "I know what you are going through" though I can only imagine it must be extremely tough.
Sorry you are feeling so rough atm. I do agree with some previous posters that it sounds like you may well have a degree of PND. The feelings of guilt, inadequacy, feeling overwhelmed and feeling criticised by your babies are quite classic signs of depression, unfortunately. Please remember that your babies are way way too young to be trying to be naughty or manipulative; it sounds like you are projecting your own fears on to them.
I am sorry you have had so little joy with your HV. Has she ever done a PND questionnaire with you? Do you always have the same one at clinic? Otherwise I would strongly agree with Vict17 that you see your GP. The starting point medical treatments for PND would be ADs and/or counselling.
Other things you can do to help are: getting out, getting a break from your babies, getting some exercise, sleeping/eating as well as you can, relaxation/meditation.
I know all these seem like a very tall order with the double whammy of looking after two babies and feeling depressed, but it is time for you to put yourself first, for the sake of you and your babies. It sounds like you desperately need a break - stuff the housework/cooking etc - your husband can do that, or hire a cleaner and order takeaways if he really doesn't want to help out.
How well are the little ones sleeping? If they wake at night, could your husband either feed them at night, or do the last evening or first morning feeds? I remember from a previous thread that you felt that your husband wasn't helpful when he did do his bit - I think you just need to get some earplugs and just leave him to it to manage for himself - once he is left to it, he will learn how to do it properly and smoothly.
Take care
x