Do you know what? I would say give yourself a break - you are breastfeeding and dealing with two small DC's whilst surviving on very little sleep. The last factor alone has been shown to spell disaster in terms of controlling appetite and cravings for all the things you shouldn't be eating!
For the time being I would try and put the focus on eating as healthily as possible, squeezing in exercise when you can. Rather than trying to lose weight, make sure you don't gain any more. Enjoy your newborn! Then plan to really go for the weight loss when you are sleeping properly and probably not breastfeeding. This should be such a short time, nothing in the scheme of things.
Re diet, low GI food and plenty of lean protein are key...think healthy rather than low calorie. Plenty of veg and some fruit.
Eggs and wholegrain toast or porridge and fruit for breakfast rather than cereal/White toast and jam.
Tuna/chicken/eggs/baked beans for lunch but with a salad/wrap or baked potato rather than a sandwich with lots of spreads/Mayo.
More lean meat or fish for dinner with stir fried/roast/steamed veg and a small portion of carbs - avoid refined ones such as pasta and white bread as far as you can though.
Include protein in snacks if you can too...a palmful of nuts, a hard boiled egg, some Greek yoghurt with berries, a skinny latte, a couple of squares of dark chocolate, miso soup, half an avocado, a small banana. These will all keep you feeling full and energised and hopefully away from the biscuits!
Try and do at least 30 minutes of exercise every day...a brisk walk with the buggy will do, a swim, yoga or exercise DVD session even better if/when you can.
If you follow the above you should feel much better for it and be in a great place to further adjust your diet and exercise regime when life is a bit calmer and you are sleeping better and can focus on yourself more?
Good luck 