Can you hire a teenage mothers helper to come a few afternoons a week (maybe afterschool or if you can find a homeschooler, during the day) to entertain your 2 older kids? They may see it as such a treat & it will give you a huge break. What about hiring someone to come clean the house once a week for a few months? Even ask for this as a gift from you mom, since she can't come. It may sound extravagant, but it will keep you sane.
As for the hospital time, I don't have a lot of advice. But, I do have a 2yr old (just turned 2), and remember, they're SO much more resilient than we realise. I almost never leave dd, and even today, my dh & I went to a birthday party & the movies, we were gone from 3:30-11:30pm & she was FINE. Never cried for us, was happy the whole time w/my sister. I think we always think they're going to be so much more upset that we're gone then they really are. I think if she comes to visit you in the hospital, she may cry when she has to leave, but she'll be okay. She'll be sad to leave, but she'll recover. We all do. Most of us have siblings & were left while mom was away in the hospital & we all made it through
Hope everything works out well for you!!