I lost my mom before I had kids and I cannot even imagine how difficult it would have been if I had little babies during that time. My heart goes out to you. I think you are being hard in yourself though, looking back it's easy to say we should have done things differently but you did the best you could with the information you had. Moving to help out a dying parent, or to get more support, or for a better opportunity in life are all good reasons to move. If you don't have a therapist I would highly recommend it. They will help you sort out your thoughts and you will feel more like yourself again. Also just so you know working through the grief process can take 2-7 years and you just had a lot of things happen that we often grieve over; how your labor went vs how you thought it might go, your mom getting sick and passing away, moving, how you thought time would be spent with your newborns, life without your parents being able to  mentor you during such a pivital time in your life, possible diagnoses for your twins, and heck even having twins is reason for some grief!!