I really really feel for you. Having a baby is hard enough in a healthy R. In your sitch, with toddler twins, and a WAH... I honestly think you are amazing for coping the way you do.
Can you get some help during the day or overnight? Friends, relatives, a babysitter or a baby nurse who can give you a chance to rest? Who is watching you for PPD symptoms?
I hope you are able to get some support. Anyone in your sitch would need it...